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and educational purposes, is the result of independent research, and 

does not necessarily reflect a position of NSA/CSS or any other U.S. 

government entity.

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Cover: Letter from British General Henry Clinton to General John 

Burgoyne with hourglass-shaped mask revealing true message. Clements 

Library, University of Michigan
Revolutionary Secrets:

Cryptology in the 

American Revolution

Jennifer Wilcox 

Center for Cryptologic History

National Security Agency

2012

3

I

n the late summer of 1781, General George Washington finally

saw an opportunity to take New York City away from the British. Virtually from the beginning of the War for Independence six

years earlier, the British had held this key city, and Washington had

long desired to take it into American hands.Washington laid siege to

the town all summer. With the expected arrival of Admiral de Grasse

and ships of the French fleet along with an additional 3,000 French

soldiers, he believed he finally had his chance. But on August 14, he

changed his mind and turned his eye to Yorktown, Virginia.

Washington received intelligence, gained partially through the 

decryption of captured British messages, that gave him the assurance 

he needed to complete his move on Yorktown.

Communication plays an important role in both a country’s 

diplomacy and its wars. Keeping those communications secret and 

understanding the adversary’s communications can make the crucial 

difference in a leader’s actions and abilities.

At the time of the American Revolution, both the British commanders and the American rebels practiced a variety of methods to 

keep their written communications secret. Both turned to invisible 

inks, hidden messages, and secret writing in the form of ciphers and 

codes.

Revolutionary Secrets: 

Cryptology in the 

American Revolution
4

Cryptography—the use of ciphers and codes—makes messages 

unintelligible to an adversary by the use of keys and lists. Ciphers

rearrange letters or change individual letters into a different letter, number, or symbol based on a prearranged setting known as a 

key. Codes change entire words or phrases into other words, number 

groups, or symbols based on a list or a book. To decrypt the secret 

messages, the receiver needs access to the original key, list, or book.

Theoretically, the adversary wouldn’t have the original source and 

therefore could not understand the message even if it were captured.

Solving a message without having the original key or list—cryptanalysis—has been employed by governments and militaries for as 

long as people have used cryptography to make messages secret.The 

ability to capture and read the enemy’s communications provides 

invaluable information for a military commander. With foreknowledge of an adversary’s intentions, leaders can develop counteractions 

and turn a battle in their favor.

This is the story of revolutionary communications and cryptologic secrets and the role they played in America’s war for independence.

The Battles Begin

Even before the first shots at the Battles of Lexington and Concord, Paul Revere had a private code system in place: a visual signaling system. Revere arranged to use two lanterns in Boston’s North 

Church to send a signal. This code was understood only by Revere 

and his friends in Charlestown. Seeing the lamps across the bay, his 

compatriots knew that the British regulars were crossing to Charlestown over the Back Bay and sent out riders to warn Sam Adams and 

John Hancock in Lexington. The signal was in place in case Revere 

were unable to cross the water himself to give the warning.

The early warnings of the patriotic rebels, initiated by the lantern 

code, helped enable a colonial victory at Concord. With knowledge 

that the British regulars were coming, the colonists pulled their militia forces together and successfully engaged the British at the North 

Bridge in Concord. They also had time to remove most of their 
5

supplies from Concord to safe places. Finally, the forewarning allowed 

Adams and Hancock to escape capture.

Although the British lost the early battles at Lexington and 

Concord, they had every reason to believe they would win the war. 

They had superior numbers, experience, and capabilities. They also 

had the support and assistance of some loyal inhabitants.

“Sympathetic Stain”

A few weeks after the battle in Concord, a British loyalist named 

Benjamin Thompson used invisible ink to send secret information to 

British headquarters in Boston.

The use of invisible inks is an ancient art, and the idea of disappearing

writing was not new at the time of the American Revolution. Giovanni

Battista Porta included several recipes for secret inks in his works of the

The Midnight Ride of Paul Revere. National Archives
6

late 16th century.

1 The practice of invisible writing was often included

in cryptologic skills until WWII when the technique fell more under the

auspices of covert operations than cryptographic methods.

After the Battles of Lexington and Concord,Thompson learned 

of some military plans in New England from conversations with 

well-placed patriots. He never named his sources, though he stated 

the information came “from a Field officer in the Rebel Army (if that 

mass of confusion may be called an Army) & from a member of the 

Provincial Congress that is now setting at Watertown.”

2

To relay his information, Thompson used a method Porta 

described to create an invisible ink: gallotannic acid. The Redcoats 

used ferrous sulfate to reactivate the ink.3

Thompson also used a common technique when writing with 

“sympathetic stain,” as invisible ink was sometimes called. He wrote 

an ordinary message in plain ink to be read if the message were intercepted by the enemy. The dark ink included nothing suspicious. It 

was merely a request to deliver some papers and obtain a receipt.

Thompson’s real message, once revealed, detailed how many men 

the Colonists hoped to raise and that their first movement would be 

against Boston. He then revealed that the Colonists would apply to 

European powers for assistance almost immediately.

 4

What may have seemed odd, and might have given the game 

away had anyone other than the British received this message, is that 

the visible portion in dark ink covered barely half a page and yet there 

were three pages enclosed in the letter.

Loyal to the crown, Thompson left his wife at the outbreak 

of the war to serve General Gage as a colonel in the loyalist army. 

When the British evacuated Boston, he moved (without his wife and 

daughter) to London where he became an assistant to Lord George 

Germain,5

 the secretary of state for the American Department. After 

the war, his work as a scientist gained prominence. Today, Sir Benjamin Thompson, Count Rumford, is known for his work in thermodynamics as well as other scientific endeavors. Less known is his 

secret involvement at the opening of the Revolutionary War.
7

Benjamin Church, British Spy

Not all of General Gage’s spies fared as well as Benjamin Thompson. Dr. Benjamin Church’s fate was less than glorious.

Dr. Church was perhaps General Gage’s most highly placed spy. 

He was a member of the Sons of Liberty and the Committees of 

Correspondence and Safety in Boston. He was elected as a delegate 

to the Massachusetts Provisional Congress and a liaison to the Continental Congress. General Washington named him chief physician 

of the Continental Army, effectively the surgeon general. And all the 

while he spied for General Gage.

Church was one of the spies who provided information about 

the military supplies held in Concord. It was this information that 

prompted Gage to move his men to Lexington and Concord, which 

led to the first shots of the war.

Dr. Benjamin Church. National 

Library of Medicine
8

However, when the war began, Church, unlike Benjamin Thompson, continued to work with the patriots and shared what he learned

with Gage. It was an encrypted letter that brought about his downfall.

The former mistress of Godfrey Wenwood, a Newport, Rhode 

Island, baker, approached Wenwood in August 1775. She asked him 

Cipher message from Dr. Benjamin Church. George 

Washington Papers, Library of Congress
9

to help her get in touch with some British officers so she could give 

them a letter. Suspicious,Wenwood convinced her to leave the letter 

with him to pass on. Instead, he gave the letter to a friend who opened 

it to discover cryptic writing of letters, symbols, numbers, and Greek 

characters. Unable to understand it, he gave it back to Wenwood who 

kept it while trying to decide what to do. When Wenwood received 

a message from the woman complaining that he hadn’t forwarded 

the letter, he became even more suspicious. He went up the chain of 

command and in September 1775 presented the enciphered letter to 

George Washington.

The mistress was brought before Washington, and under interrogation she admitted the letter came from Dr. Church. Washington was stunned by this news since the doctor was a highly valued 

and trusted man in his army. He called for the doctor to explain the 

incriminating evidence. Church admitted he had written the letter, 

but claimed it was to his brother and of little import.The letter, however, was addressed to Major Cane of the British military. Church 

refused to decrypt the letter and prove his innocence. 

Washington searched for someone to decipher the message. Dr. 

Samuel West, a pastor and former classmate of Church’s, took on 

the task. Elbridge Gerry, a member of the Massachusetts Provisional 

Congress (and later the fifth vice president of the United States) and 

Elisha Porter, a colonel in a Massachusetts regiment, also worked on 

it as a team.They both came up with the same solution.

The cipher used a simple monoalphabetic substitution. Each 

letter of the alphabet was replaced by a different letter, number, or 

character. For example, Church used the number 9 to represent the 

letter A, a capital W replaced B, capital S was C, the Greek letter Phi 

(Φ) was D, and so on.6

 Because the actual, or plain text, letter was 

always replaced with the same cipher character, the system was fairly 

easy to solve. Church may have believed the common misconception 

that the use of nonalphabetic characters made a substitution system 

more difficult to decipher. West, Gerry, and Porter solved the message in only a day or two. Washington received both decryptions on 

October 3.
10

The monoalphabetic cipher revealed that Church was providing 

General Gage with information on American ammunition supplies;

rations; recruiting; a proposed attack on Canada; artillery in Kingsbridge, New York; troop strength in Philadelphia; and the general 

mood of the Continental Congress.

Presented with the decryption, Church claimed he was trying 

to show the British the strength of the Americans in order to deter 

them. He had in fact greatly exaggerated the Americans’ numbers 

and used this as proof of his motives. Church’s words only made the 

patriots more thoroughly convinced of his guilt. However, the depth 

of Church’s dealings with Gage was not known until the 20th century. Washington knew only of this one encrypted letter, but it was 

enough to seal Church’s fate.

After being jailed, and a prisoner exchange refused, Church was 

finally exiled to the West Indies in 1780. The ship he was on sank 

and Church was never heard from again.7

Hiding Secrets

The loss of a valued officer was only one of Washington’s setbacks 

in the first few years of the war. The British, under the command 

of General Howe, took control of New York harbor in the summer 

of 1776. Washington knew that if he were to defeat the British, he 

needed to know the current status of their troops and supplies as well 

as have foreknowledge of their intentions. He needed a volunteer to 

enter the British lines and spy. Nathan Hale agreed to go. 

Unfortunately, Hale was recognized as a rebel and arrested.

Incriminating notes were found hidden in his boots and he confessed 

to being a soldier in the Continental Army. He was accused of spying 

and immediately sentenced without a trial to hang the next morning. 

Hale’s attempt to hide his notes in his shoes was a feeble attempt at

best.The British were far better at hiding messages.They secreted communications inside canteens, silver balls the size of bullets, feather quills,

and even within ordinary-looking letters. Generals Burgoyne, Howe, and

Clinton used a few these techniques prior to the Battles of Saratoga.
11

Burgoyne planned to cripple the Continental forces by moving 

his troops from Quebec to Albany. A second column would come 

through the Mohawk Valley in central New York, while a third British force, under William Howe’s command, would come north from 

New York City. When the British controlled the Hudson River valley, they would sever New England from the rest of the colonies.

However, this was not to be. General Howe decided to change 

the plan.

After George Washington’s recent victories in Trenton and Princeton, New Jersey, Howe sought and received permission from Lord

Germain to take Philadelphia. Howe made Burgoyne aware of his

intentions to move to Philadelphia instead of moving north toward

Albany via a message hidden inside a quill. He inserted the long, narrow, messages into a large, hollow quill feather (see next page).

Map of General Burgoyne’s plan to capture Albany
12

General Howe’s quill messages and detail. 

Clements Library, University of Michigan


13

Part of the note hidden in the quill said:

Washington is waiting our motions here ... My intention is for Pensilvania where I expect to meet Washington, but if he goes to the Northw.d ... you can keep him 

at Bay, be assured I shall soon be after him to relieve 

you. ... S.r Hen.y Clinton remains in the command here, 

& will act as occurrences may direct. Putnam is in the 

Highlands with about 4000 men. - Success be ever with 

you. Yours. & [etc.] WHowe

8

The Hourglass Mask

Distressed that he would not have the support he needed,

British general Burgoyne attempted to change Howe’s mind, but

to no avail. Even Sir Henry Clinton believed Howe’s move unwise. 

In another secret message to Burgoyne, Clinton expressed his concern. However, his words are cleverly disguised as approval.

You will have heard, Dr Sir, I doubt not long before 

this can have reached you that Sir W Howe is gone 

from hence. The Rebels imagine that he is gone to the 

Eastward. By this time however he has filled Chesapeak 

bay with surprize and terror. Washington marched the 

greater part of the Rebels to Philadelphia in order to 

oppose Sir Wm’s army. I hear he is now returned upon 

finding none of our troops landed but am not sure of 

this, great part of his troops are returned for certain. I 

am sure this countermarching must be ruin to them. I 

am left to command here, half of my force may, I am 

sure, defend everything here with much safety. I shall 

therefore send Sir W 4 or 5 Bat[talio]ns. I have too 

small a force to invade the New England provinces;

they are too weak to make any effectual efforts against 

me and you do not want any diversion in your favour. 

I can, therefore very well spare him 1500 men. I shall 

try something certainly towards the close of the year, 

not till then at any rate. It may be of use to inform you 
14

that report says all yields to you. I own to you that I think 

the business will quickly be over now. Sr W’s move just at 

this time has been capital.Washingtons have been the worst 

he could take in every respect. Sincerely give you much joy 

on your success and am with great Sincerity your HC.9

The actual message, however, was hidden within. It can be revealed

through the use of a mask. A sheet of paper with an hourglass shape cut

from it could be placed over the full letter allowing only a smaller portion

of the writing to be visible. With the mask in place, the message Henry

Clinton relays is vastly different from the full letter: 

Sir W Howe is gone to the Chesapeak bay with the greatest

part of the army. I hear he is landed but am not certain. I am left

to command here with too small a force to make any effectual

diversion in your favour. I shall try something at any rate. It may

be of use to you. I own to you I think Sr W’s move just at this

time the worst he could take. Much joy on your success.10

These masked messages may have been England’s most secure 

form of written communication because they provided no discernable patterns; however, they were difficult to construct.They required 

two parts: the letter and the mask. The mask is laid over the blank 

paper, and the true message is written within the open space. Then 

the mask is removed and the rest of the letter is composed around the 

true message. This can be quite difficult since the letter must make 

sense when read even without the mask. However, if done properly, it 

can effectively protect secret messages.

Despite the fact that Burgoyne received these and other hidden

messages without issue, he still failed to take Albany. The lack of reinforcements and his determination to still move forward resulted in his

defeat at the Battles of Saratoga. Burgoyne was forced to surrender to

General Horatio Gates on October 17, 1777.This was the first major

battle won by the Continental Army and a turning point in the war. 

With this victory, the French openly sided with the Americans.

On February 6, 1778, the French and Americans signed the Treaty 

of Alliance.
15

Clinton letter to Burgoyne with hourglass-shaped mask 

revealing true message. Clements Library, 

University of Michigan
16

New York’s Spy Ring

In the late spring of 1778, George Washington set up a perimeter around New York City, but the harbor and waters still belonged 

to the British, now under the command of General Clinton. The 

French opted to engage the British in the West Indies rather than 

on the American coast. Although the French action was helpful to 

the United States because it pulled British attention and forces away 

from New York, it wasn’t precisely what the Americans preferred.

Washington wanted New York, and to get it he needed information. After the failed espionage attempt by Nathan Hale, Washington knew what he really needed was a resident inside New York.

Someone in the city who put on the airs of a loyalist would not stand 

out and could gather better information. Washington also needed a 

transmission route to get the information safely out of New York and 

into his hands.

In the summer of 1778, Washington ordered Major Benjamin 

Tallmadge to create a spy network.

Tallmadge was born and raised in Suffolk County, NY, and 

attended Yale College. When the war began, Tallmadge joined the 

Continental Army and participated in several battles with Washington, including the Battles of Long Island, Brandywine, and 

Monmouth.

Tallmadge knew that a coordinated network of well-placed spies 

and couriers, all working under specific and clear direction, could 

take the information from the city without throwing suspicion 

on its members. For his agents, Tallmadge, who took on the code 

name John Bolton, turned to the neighbors he knew and trusted in 

Setauket, NY. This group became the Culper spy ring.

Sailor, Merchant, Landlord, Spies

Caleb Brewster was a childhood friend of Tallmadge, but he 

wasn’t recruited into the spy ring. In fact, he offered his services to 

Washington even before the Culper spy ring began.
17

Brewster had been a whaleboatman before serving in the Continental Army. In his free time, he took whaleboats and crossed Long 

Island Sound to harass the British on the opposite shore. He offered 

to provide Washington with British naval movements, troop numbers, the status of their provisions, and any signs of embarkation.

Washington was happy to have the information.

Brewster was the clear choice to carry Tallmadge’s information

requests from Connecticut across the Sound to Abraham Woodhull in

Setauket.

As another childhood friend, Woodhull was Tallmadge’s first

recruit. Known by the code name Samuel Culper, Woodhull began

providing Tallmadge with information from New York City since

he made routine trips there. Despite being devoted to the cause, 

Woodhull was not made to be a spy. Ever fearful of being discovered, Woodhull insisted on anonymity. After a few close calls

with the British, he decided to stay out of the city. However, he

knew how important the work was to Washington and took pride

in being a part of it. He found a man to fill his place in New York

City while he remained in Setauket gathering information from

Long Island.

Tallmadge gave his requests to Brewster, who took them

across the Sound to Woodhull. Woodhull reviewed them and gave

instructions to Austin Roe. Roe was the spy ring’s primary courier. 

As a tavern owner in Setauket, he had reason to travel the fifty-five

miles between New York City and Setauket to pick up supplies

for his business. He carried Woodhull’s instructions, which were

frequently hidden between the lines of a shopping list in invisible

ink, to New York City. Once in town, he would pass the request to

Robert Townsend.

Robert Townsend, Woodhull’s replacement in the city, couldn’t 

have been a better choice. He resided and worked in the city as the 

owner of a dry goods store. However, he too was very concerned 

about his safety should his identity be discovered. Even Washington knew him only by his code name, Culper Jr. Handwriting analysis and comparison of activities and places by the author Morton 
18

Pennypacker in the 1920s finally revealed that Culper Jr. was Robert 

Townsend.

Townsend was known to write articles for the King’s newspaper Rivington’s Royal Gazette. Those British soldiers whose names 

and military activities appeared in British papers seemed to be promoted more quickly, so officers were eager to share their stories with 

Townsend, an apparent loyalist. They would discuss their exploits 

in the coffee house conveniently located near Rivington’s press and 

Townsend’s store. 

 Roe passed on to Townsend the request for specific information on the British. At his first opportunity, Townsend took the message to his private quarters and used a reactivation agent on the note, 

causing the real instructions to appear from the invisible ink.

Jay’s “Stain and Counterpart”

The ink used by the spy ring, as well as by others under General 

Washington’s command, was a concoction developed by Dr. James Jay. 

Jay, a physician born in New York, moved to England in 1762 

but remained loyal to his homeland. Before the outbreak of the war, 

Jay realized a secret form of communication was needed. After much 

experimentation, he came upon a successful mixture. It was a twopart solution: one chemical acted as the invisible ink and another 

made it visible.

11

George Washington particularly liked Jay’s invisible ink and 

directed his spies to make use of it. In a letter to Benjamin Tallmadge, he wrote: “I send twenty guineas and two fials containing 

the stain and counterpart of the stain for C__ Jr. which I wish may 

be got to him with as much safety and dispatch as will conveniently 

admit of.”

12

Washington also believed information should be transmitted, as 

Jay recommended, hidden between the lines of an innocent letter. 

The “shopping list” used this method. However, Townsend preferred 

to respond using blank paper. He then hid the stained page within 
19

a ream of paper at a specific location. This method allowed Roe to 

return to Setauket with the papers as part of his supplies.

Riding the fifty-five miles back, Roe stopped at Woodhull’s farm.

Woodhull, signing his letters as Culper Sr., included his own comments and information separately in black ink and partially in a code 

that Tallmadge created in 1779.

Codes replace words with other words, numbers, or even symbols. A wide variety of codes exist, but Tallmadge’s was a simple 

replacement of one number for one word. Tallmadge’s code list consisted of more than 763 terms and names. Like several other codes,

it was based on Entick’s Spelling Dictionary, but he selected the words 

to be included. It was a one-part code both alphabetic and numeric 

in order. A was number 1 and Zeal was 710. At the end he added 

additional numbers for people, place-names, and dates.13

Culper Jr. (Townsend) made good use of the system. For 

example, the last two sentences from a coded message of August 

1779 to Tallmadge read, “The Renown and Daphne Eli 625 only 

592.431.680.282 Rqlv – In 379 pizv 683.281 possible acxi 707.1.526 

Eggqwpv 431.625 situation 431.625.655 – Yours 723.”This decodes 

to say, “The Renown and Daphne Eli [are] the only ships of war in 

port. In my next will if possible give you a particular account of the 

situation of the troops. Yours Culper Junior.”

14

Culper Sr. (Woodhull) also used the code, but with less effect.

Most of his letters were written in plain text with only a few code 

numbers included. A typical letter from Woodhull begins as this 

November 1780 message does:

729 427 ef 1780.

Dear Sir, 

Your favour of the k instant is received and observe the contents. In answer to your first question, I again informe you 

that I was at 727 about the 20 of last month. I then with 

the advise of C__ Junr and others transmitted you the most 

accurate account of the embarkation of Gen Mathews.15
20

The code simply states that Culper Sr. was writing from Setauket 

(729) on November (427) 12th (ef). He says he received Tallmadge’s 

letter of the 5th (k) and that he was at New York City (727) about the 

20th of last month. Most of the message is in plain text.

Having added his information to that of Townsend’s, Woodhull 

delivered the missives to Brewster. However, because the process of 

requesting and obtaining the information took days,Woodhull didn’t 

always know when and where Brewster would be found. Another 

member of the ring provided the necessary information through a 

unique signaling system.

Anna Strong, known as Nancy, lived on a farm on Long Island

Sound within sight of Woodhull’s farm. Strong hung a black petticoat

on her clothesline to indicate that Brewster was in place. Then she

would hang between one and six handkerchiefs to indicate in which

of six possible coves he was waiting. Though the line was in sight of

anyone who wished to look, the code meant nothing to the British.

Once Brewster had the secret messages that were written in code 

and invisible ink, he took them across the Sound to be carried to 

Tallmadge and on to General Washington.

This very circuitous route by which messages traveled—from 

Connecticut across Long Island Sound to Setauket, to New York 

City, back again, and only then to George Washington—though 

successful, frequently took too long. Washington complained that 

the information was quite valuable, but by the time he received it, it 

wasn’t as useful as it could have been. In a letter to Tallmadge, Washington implores,

It is my further most earnest wish, that you would press him 

[Culper Jr.] to open, if possible, a communication with me 

by a more direct route than the present. His accounts are 

intelligent, clear, and satisfactory, consequently would be 

valuable, but owing to the circuitous route through which 

they are transmitted I can derive no immediate or important 

advantage of from them, and (as I rely upon his intelligence) 

the only satisfaction I derive from it, is, that other accts are 
21

either confirmed or corrected by his, after they have been 

some time received.16

This situation was a constant complaint of Washington’s, but it 

was never resolved to anyone’s satisfaction.Woodhull refused to communicate with anyone he couldn’t personally vouch for. On one occasion Townsend forwarded a message through a courier who, being in 

enemy territory, posed as loyalist. The message he carried was intercepted. Fortunately, it was intercepted by a patriot who believed the 

courier to be a Tory and gave the message to Washington. An alternate route was never further pursued.

Culper Information Aids Washington

Most of the information Culpers Sr. and Jr. provided concerned 

the number of British troops, ships, and provisions in New York City 

as well as the general spirits of the regulars and Tories. However, on 

one occasion, the Culpers warned that a man working with Washington was in fact loyal to the mayor of New York City and therefore 

Information route of Culper spy ring
22

should not be trusted.“Mr C Junr informed me at our intervene that 

Christopher Dyeink [Duychenik] ... of 10 [New York] ... is amongst 

you and is positively an agent for David Mathews Mayor of 10 under 

the direction of Tyron [major-general in British Army and governor 

of the Province of New York.]”17

Possibly the most valuable information Townsend sent was in 

July 1780.Washington, knowing the French fleet was about to arrive 

in Newport,Rhode Island, asked for any information concerning the 

British activities in New York City and Long Island. Within days 

of the request, the message went from Tallmadge to Caleb Brewster, who took it across Long Island Sound to Austin Roe. Roe rode 

virtually nonstop from Setauket to New York City and waited while 

Townsend gathered the information.

Townsend learned that the British had gathered 8,000 troops 

and sailed to the north side of Long Island. British general Henry Clinton planned to attack the French before they became

entrenched.

Clinton knew of the imminent arrival of the French through his 

own source, Benedict Arnold.18 In a letter to his superiors in England, Clinton wrote, “Immediately on my arrival from the southward 

I received, from such authority [Arnold] as I should have risked an 

action upon, that the French fleet and 6,000 troops were expected 

at Rhode Island.”

19 Benedict Arnold, a trusted major general in the 

Continental Army, received his information directly from Washington’s headquarters. It was not the first correspondence between 

Arnold and Clinton, nor would it be the last, but it did inspire Clinton to make a move against the French fleet. He began his preparations to move men out of New York City. It was these actions that 

Townsend reported back to Washington.

However, Culper Jr.’s usual means of writing with invisible ink 

on a specific piece of paper in a stack and carrying the stack back with 

other goods would have delayed the response by a day. Townsend 

decided instead to write a short message to a known Tory saying that 

the goods he had requested were not currently available.

20 This would 

explain why Roe returned without supplies, should he be stopped 
23

along the way. The real information was written in the “sympathetic 

stain” on that letter. That same day Austin Roe rode the fifty-five 

miles back to Setauket and delivered the letter to Woodhull.

Woodhull’s accompanying letter to Caleb Brewster emphasized

the importance of Townsend’s information.“The enclosed requires

your immediate departure this day. By all means let not an hour

pass: for this day must not be lost. You have news of the greatest

consequence perhaps that ever happened to your country.”

21

Brewster took Townsend’s and Woodhull’s letters back across the 

Sound. Because he didn’t know the current location of Major Tallmadge, Brewster gave the information to a dispatch rider to deliver 

them directly to headquarters. Another copy made its way to Tallmadge. At Washington’s headquarters, Alexander Hamilton received 

the messages the following afternoon (Washington was not at headquarters at the time).The entire procedure from Washington’s initial 

request to Hamilton’s receipt took ten days.

 Hamilton, who was acquainted with the Culpers’ methods, used 

the reactivation agent and read the letter. He forwarded the news 

to the Marquis de Lafayette, who was on his way to Newport to 

meet the French fleet.When Tallmadge received the information, he 

immediately sent it on to General Washington.

With this new information, General Washington knew he needed to keep Clinton from getting to Newport and the French fleet.

He also knew, as did Clinton, that the reduction of forces in New 

York left the city vulnerable. Though Washington wanted to take the 

opportunity to attack, he knew his troops were too few to succeed.

However, in order to protect French lieutenant general Rochambeau’s arrival in Newport,Washington needed only to stop Clinton’s 

movement to Rhode Island.

Washington moved his troops toward New York in a feint to draw 

Clinton’s attention.“During this time,”Clinton reported,“Washington, by a rapid movement, had, with an army increased to 12,000 

men, passed the North-river, and was moving towards King’s-bridge, 

when he must have learned that my armament had not proceeded to 
24

Rhode-Island. He (I apprehend in consequence of this) re-crossed 

the river, and is now near Orange Town.”

22

Washington’s ruse worked. Clinton called back his troops to protect New York City from an attack that would never come. And thus 

Rochambeau and the French fleet’s arrival in Newport went unchallenged.Washington then began to make plans to join forces with the 

French for a real attack on New York City. 

Benedict Arnold’s Treason

As Townsend and Woodhull were hurrying to gather the information Washington requested, Benedict Arnold was plotting to sell 

West Point to the British. For more than a year Arnold had been 

providing the British with information.

While in command of Philadelphia, Arnold met a beautiful 

young woman, Margaret “Peggy” Shippen, the daughter of a prominent loyalist family. She and her sisters had previously caught the 

attention of British officers stationed in the town. Among those men 

was John Andre, adjutant-general in the British Army and chief of 

its intelligence service. When he left Philadelphia with the British 

troops, Peggy managed to maintain communications with him.

Despite a twenty-year age difference, Arnold sought and eventually won Peggy’s hand. Soon after their marriage in April 1779,

Arnold began a secret correspondence through John Andre with the 

British general Sir Henry Clinton.

Page, Line, and Word: Book Codes

 Arnold communicated with the British using book codes and 

ciphers in addition to invisible ink. Book codes and ciphers (sometimes called “dictionary codes”) were quite common at the time of 

the Revolution.They can provide excellent security if the sender and 

the receiver each have access to the same edition of the book and the 

book contains many of the necessary words. This generally requires 

lengthy volumes on a subject similar to the topic to be encoded.

Ideally, the most commonly used words could be found repeatedly 
25

throughout the book, allowing several choices to encode the same 

word. Book codes, however, are a bit cumbersome. When the sender 

attempts to encode, locating the required words within the text can 

be time consuming, assuming the word is used in the book at all.

Arnold’s book of choice was a legal tome: Blackstone’s Commentaries 

on the Laws of England. 

Although the actual process varies, Arnold used a standard 

encoding procedure in which a three-number code group replaces a 

word. The numbers represent the page, line, and word count in that 

line; for example, 43.23.12 indicates the twelfth word on the twentythird line of page 43.

However, Blackstone’s law book contained few of the words 

Arnold needed to relay military information, and much of his message was tediously ciphered.To use a book as a cipher tool, individual 

letters spelling out a word are located throughout the book.The code 

group represents the page, line, and letter count. To indicate a letBenedict Arnold. H. B. Hall, Anne S.K. Brown Military

Collection, Brown University Library
26

ter instead of a word, the final number has a line drawn through 

it: 43.23.12 indicates the twelfth letter on the twenty-third line of 

page 43. This book cipher proved so tedious that Arnold and Andre 

quickly began using Nathan Bailey’s Dictionary.

Dictionaries contain the all necessary words. However, each word 

is listed only once and therefore frequently used words will have the 

same code group appearing repeatedly in messages. Also, they are in 

alphabetical order. This makes the words easy to locate, but it also 

gives an adversary an advantage at guessing a word. The code 6.1.14 

indicates a page early in the dictionary; therefore, the word begins 

with a letter at the beginning of the alphabet. The use of a dictionary over another book becomes obvious in a coded message as well.

Instead of indicating which line, the second number indicates the 

column.Thus 6.1.14 represents the fourteenth word listed in the first 

column on page 6.When the middle number is always either 1 or 2,

a dictionary code is in use.

West Point for Sale

In a July 15, 1780, coded message using a dictionary code, Benedict Arnold proposed the sale of West Point. (In his letter, the middle 

number of the code group is always an 8 or 9 because Arnold added 

seven to each of the numbers.) 

West Point was an important fortification on the banks of the 

Hudson River, valuable not only for its strategic location but also 

for its supplies. (The U.S. Military Academy would not be officially 

established there until 1802.) Arnold knew West Point would be a 

significant asset to the British. If he had command of the garrison, he 

could turn it over to the British ... for a price.

Decoded, Arnold’s message reads as follows (italics added to 

indicate the words in plain text):

Two days since I received a letter without date or signature, 

informing me that S. Henry —— was obliged to me for the

intelligence communicated, and that he placed a full confidence in the sincerity of my intentions,etc. etc. etc. On the 13th 

28

paid to me or my heirs in case of loss; and, as soon as that shall 

happen, —— hundred pounds per annum to be secured to me 

for life, in lieu of the pay and emoluments I give up, for my

services as they shall deserve – If I point out a plan of cooperation by which S. Henry shall possess himself of West Point,

the Garrison, etc. etc. etc. twenty thousand pounds Sterling I 

think will be a cheap purchase for an object of so much importance. At the same time I request a thousand pounds to be paid 

my Agent – I expect a full and explicit answer – The 20th I

set off for West Point. A personal interview with an officer 

that you can confide in is absolutely necessary to plan matters.

In the mean time I shall communicate to our mutual friend 

S______y [Stansbury, the courier] all the intelligence in my

power, until I have the pleasure of your answer. 

Moore [Arnold] 

July 15th [1780] 

To the line of my letter of the 13th I did not add seven.23

Clinton responded with a message agreeing that the garrison 

with 3,000 men, artillery, and supplies was worth £20,000.24 He 

didn’t, however, agree to compensate Arnold with an additional 

£10,000 regardless of how events turned out.

Arnold did not always use the dictionary code. His August 30 

reply to Clinton is disguised as business correspondence. He writes 

signing the name Gustavus and refers to himself as Mr. Moore. He 

opens by saying he received Clinton’s message and expects to reply in 

full at a later date.

... and to procure you an interview with Mr M___e [Moore] 

when you will be able to settle your commercial plan I hope 

agreeable to all parties. Mr M___e assures me that he is still 

of opinion that his first proposal is by no means unreasonable and makes no doubt when he has a conference with 

you that you will close with it. He expects when you meet 

that you will be fully authorised from your house: that the 

risques, and profit of the co-partnership may be fully and 

clearly understood.
29

A speculation might at this time be easily made to some advantage with ready money, but there is not the quantity of goods

at market which your partner seems to suppose, and the number of speculators below I think will be against your making an

immediate purchase. I apprehend goods will be in greater plenty

and much cheaper in the course of the season; both dry & wet

are much wanted and in demand at this juncture, some quantities are expected in this part of the Country soon.

Mr M___e flatters himself that in the course of ten days he 

will have the pleasure of seeing you. ...25

Andre and Clinton would have understood the true meaning of 

Arnold’s message: Arnold still believed that his original request for

£10,000 was reasonable. The second paragraph warns that West Point

doesn’t have the number of men Clinton seems to believe, and with

the Americans (speculators) nearby, now would not be a good time to

move. The message concludes that Arnold expects things to improve

shortly and hopes to have their face-to-face meeting within ten days.26

This particular message was given to an innocent courier who 

had no knowledge of its contents or purpose. However, he was suspicious of the circumstances in which Arnold gave him the letter to 

carry. Rather than follow Arnold’s delivery instructions, the courier 

passed the message to General Parsons of the Continental Army. 

As Arnold had hoped, should it be intercepted, Parsons believed it 

was merely a commercial correspondence and thought little of it. He 

didn’t turn it over to Washington until Arnold’s treachery was known.

The Betrayal Exposed

Why Benedict Arnold chose to betray his country has long been 

debated. His desire for recognition and his need for money most 

likely played a role. The lifestyle he maintained with his young wife 

was well outside his means, causing him to go into debt. Also, in 

April 1780 he faced a court martial on eight charges for actions committed while in command of Philadelphia. Although he was convicted of only two minor offenses, this, combined with his previous 
30

perceived slights, undoubtedly further angered him. (Not only had 

General Gates failed to mention Arnold in his report on Saratoga,

but also Congress passed over Arnold while promoting junior officers in 1777.) In April, amidst the court martial, Arnold resigned as 

military governor of Philadelphia. Shortly thereafter, following up 

on Washington’s promise of a prominent position, he requested command of West Point.

 On August 3, 1780,Washington granted Arnold’s request, never 

knowing Arnold was already conspiring to give up the stronghold to 

the British.

To make the arrangements for the sale and capture of West Point,

General Clinton sent John Andre to meet with Arnold. The two 

had long been connected through the secret correspondence chain.

Though no one knows exactly what was discussed, they spoke until 

almost dawn on September 22. Arnold also passed papers concerning 

West Point’s fortifications and other details to Andre, insisting that 

he hide them in his stockings.

Arnold arranged for a friend, Joshua Smith, to escort Andre back 

to the British over a land route. He wrote passes for “John Anderson,”

the code name for Andre, and Joshua Smith to present if they were 

stopped by the American posts. Arnold then returned to his home 

near West Point.

The next day, Smith led Andre, dressed in civilian clothes, toward

White Plains, NY. Smith turned back several miles short of White

Plains, leaving Andre to continue on his own.They were past the usual

American lines, and neither expected any trouble the rest of the way.

Three volunteer militiamen stopped Andre outside Tarrytown.

Despite having the pass Arnold signed naming him “John Anderson,” Andre was searched and the papers hidden in his boot were 

discovered.The militiamen turned him in to the nearest Continental 

Army camp, North Castle. 
31

Capture of John Andre. J. Baillie. Andre is offering his watch and horse for his release.

Library of Congress
32

Major Tallmadge, who arrived at North Castle shortly after, 

immediately realized the implications of the situation. Even if “Mr. 

Anderson” stole the papers without Arnold’s knowledge, it was apparent that Arnold met with a spy for some reason. If not incriminating, 

it was highly suspicious.

Despite these suspicions, there was no proof of involvement, and 

the commander of North Castle insisted on sending a report of the 

incident to his commanding officer, Benedict Arnold. However, he 

sent the confiscated papers to General Washington.

When Andre learned the documents were being taken to General Washington, he knew he was lost. He confessed to being Major 

John Andre, Clinton’s adjutant-general. This confession proved not 

only that he was a spy, but also that Arnold was guilty. 

Arnold received the report sent to him from North Castle. He 

hurriedly ordered a horse and asked that General Washington, who 

was expected shortly, be told that he had urgent business at West 

Point. He mounted up and rode away to the nearest British outpost,

making his escape.

Washington arrived at Arnold’s home and then went to West

Point where Arnold claimed he would be. The captured documents

and Andre’s confession finally reached him.Washington must have

been stunned that his brave, trusted, and tactically brilliant general 

was in fact a traitor. He didn’t hesitate long, however, and quickly

sent Alexander Hamilton to catch up with Arnold, but Arnold was

already safely behind British lines aboard the HMS Vulture. 

Arnold’s turning shut down the Culper spy ring for some time. 

Several of the spies feared that Arnold knew their names and had 

revealed them to the British. Arnold did know that Tallmadge ran a 

network in New York City and at one point sought out their names 

on the pretext that as commander of West Point he could use their 

services as well. Fortunately, no one provided the identities to Arnold,

and the spies remained undetected. However, Washington felt the 

loss of intelligence for several months.
33

The Tide Turns for the Americans

The following summer, 1781, British general Sir Henry Clinton 

ordered General Charles Cornwallis to fortify a post to protect ships 

in the Chesapeake Bay. Clinton, along with Admiral Graves, suggested that York (later called Yorktown) might be favorable. 

Cornwallis knew that the towns of York and Gloucester, which 

lay across the York River from each other in Virginia, could not 

easily be defended. However, he agreed, “to seize and fortify York 

and Gloucester, being the only harbour in which we can hope to be 

able to give effectual protection to the line of battle ships.”

27 And so 

Cornwallis found himself forced to defend posts that “would require 

a great deal of time and labour to fortify... For York and Gloucester, 

from their situation, command no country.”

28

Meanwhile, George Washington still hoped to win back New 

York. He had been laying siege to the town all summer and hoped 

the activities in the south would draw Clinton away, thus weakening the defenses around New York. He planned an assault on the 

city with Rochambeau’s forces and the additional French forces of 

Admiral de Grasse, who was coming from the West Indies. However, on August 14, 1781, Washington learned that the French fleet 

would go no farther than Chesapeake Bay. De Grasse would use his 

fleet, and the troops it carried, to stop the British from establishing a 

stronghold at the bay.

Washington changed his mind about New York and turned his 

attention to the south. Along with Rochambeau, Washington began 

to plan an attack on Cornwallis in Virginia. Washington disguised 

their activities by playing into Clinton’s assumption that the Americans would attack New York City. He made it look as if he planned to 

move troops to Staten Island, and he set up a false camp in New Jersey knowing Clinton’s spies would report it. His deception worked;

Clinton didn’t realize the Americans’ true intentions until the French 

and American troops were well on their way south.

On August 30, 1781, de Grasse and the French fleet arrived at the

mouth of the Chesapeake Bay from the West Indies. He brought with
34

him not only 28 ships of the line and supporting frigates but also 3,000

French troops to reinforce Lafayette’s men in Williamsburg, Virginia.

For the next week, almost daily, Cornwallis sent encrypted messages to General Clinton informing him of the arrival of de Grasse 

and the number of ships involved.

Clinton intended to reinforce Cornwallis. He sent Admiral 

Graves and some of the British fleet to the Chesapeake. He would 

Washington’s route to meet Cornwallis at York

York 

Lafayette

French 

fleet Cornwallis

Washington & Rochambeau



y
35

wait for more ships and troops to arrive from Europe and then they 

would relieve Cornwallis.

The Americans intercepted a message Cornwallis sent on September 8. It described the arrival and forces of the French fleet 

between the capes of the Chesapeake. Cornwallis added to this letter 

that Washington and his troops were expected to arrive soon and that 

Lafayette was in Williamsburg. General Cornwallis also reported 

that firing was heard from the Chesapeake on September 4–6.29

The firing would have been the Battle of the Chesapeake Capes.

Admiral Graves’s British ships met the forces of the French fleet 

under de Grasse. To communicate from one ship to another, the British used a visual flag signaling system. The Americans had a copy of 

the flag code book. One of Washington’s men, McLane, had picked 

it up from James Rivington.

Rivington was the official printer for the King in New York and also

a spy for George Washington. In his Tory newspaper, Rivington’s Royal

Gazette, he reported in great exaggerated detail the losses of the Americans while he glossed over any British failures. His apparent dedication

to the Crown allowed him access to British military information.

How Rivington came to have the British flag code book is not

known, but he was believed to be an ardent loyalist and had frequent

contact with the British military in New York. Access to the book may

have come openly or secretly. Rivington turned the code book over to

McLane, but it isn’t known whether McLane got it back to the mouth

of the Chesapeake in time for de Grasse to make use of it in the battle.

In the end, with or without the flag code book, de Grasse defeated Admiral Graves. The British ships returned north, leaving Cornwallis to suffer the consequences.

Following all this, Cornwallis, in his September 8 letter, reported 

his own position (see next page).The details of the American actions 

are in plain text, but he encrypted the portion of the message revealing his own situation. “As my works were not in a state of defence I 

have taken a strong position out of the town. I am now working hard 

at the redoubts of the place.”

30

37

The intercepted letter uses a simple substitution cipher. The 

alphabet is randomly scrambled, and each letter is assigned a specific 

number between 1 and 29, less the numbers 10 and 20.

However, Cornwallis complicated the simple substitution slightly. First, he ran numbers together, separated only by periods, making 

it difficult to determine word length until it was actually deciphered.

Second, after the first encrypted sentence, Cornwallis changed to 

a different cipher alphabet for the remainder of his message. The 

original cipher and the cipher change are indicated in separate number groups that include numbers higher than 29 (i.e., 44.32.10 and 

43.32.3).

This Cornwallis message was one of several encrypted communications captured by the Americans. James Lovell in the Committee of Foreign Affairs, previously known as the Committee of Secret 

Correspondence, solved the ciphers.

James Lovell was a pioneer in cryptographic methods. He studied at Harvard and was later elected to the Continental Congress.

Shortly thereafter he was assigned to the Committee of Foreign 

Affairs. He took his assignment to the committee quite seriously 

and stayed there for five years as other members came and went.

Among Lovell’s responsibilities on that committee were the writing 

and deciphering of dispatches.

Comparing intercepted British messages taken from October 

1780 through August 1781, Lovell realized that the British made 

only minor changes to their cipher. “For, it appears to me that the 

Enemy make only such changes in their Cypher, when they meet 

with misfortunes ...”

31

In late September, Lovell sent the keys to these ciphers to George 

Washington believing they might be of assistance should the general 

have access to other intercepted messages. On October 6, in a note to 

Lovell,Washington confirmed,“My secretary has taken a copy of the 

cyphers and by help of one of the alphabets has been able to decypher 

one paragraph of a letter lately intercepted going from Lord Cornwallis to Sir Henry Clinton.”

32
38

These ciphered messages and the corroborating intelligence from

other sources gave Washington a full picture of Cornwallis’s situation. Cornwallis was desperate. Washington also had word from the

north that Clinton and his troops had not yet left New York since they

awaited favorable conditions to sail.With everything to his advantage, 

Washington moved his troops from Williamsburg toward Yorktown,

meeting little resistance along the way, and encamped outside Cornwallis’s fortifications.The Siege of Yorktown began September 28.

Completely surrounded, Cornwallis could not escape through 

the bay or by land. His only chance was to hold out until Clinton 

arrived with reinforcements. His messages to Clinton became more 

and more desperate as he reported the Americans’ encroachment and 

attacks. On October 11, he insisted in his encrypted message, “I have 

only to repeat what I said in my letter of the 3d, that nothing but a 

direct move to York river, which includes a successful naval action,

can save me.” After describing the rebel actions, he related,“We have 

lost about seventy men, and many of our works are considerably damaged; with such works on disadvantageous ground, against so powerful an attack we cannot hope to make a very long resistance.”

33 Four 

days later another cipher letter conveys the deteriorating situation 

and concludes, “The safety of the place is, therefore, so precarious,

that I cannot recommend that the fleet and army should run great 

risque in endeavouring to save us.”

34

Two days later, Cornwallis sent a letter to General Washington 

requesting cessation of hostilities in order to discuss the surrender of 

York and Gloucester. Washington was happy to comply. 

On October 19, 1781, Cornwallis’s deputy officially surrendered 

to the combined French-American forces. General Benjamin Lincoln accepted the surrender sword at Washington’s request.

The day after the surrender, Washington received British intelligence

that was still of some importance. It was an intercepted and decrypted

message from General Clinton to Cornwallis written on September 30:

I am doing everything in my power to relieve you by direct

move, and I have reason to hope, from the assurances given me
39

Surrender of Lord Cornwallis. John Trumbull. General 

Benjamin Lincoln (center, on horse) accepted the British 

surrender. Washington is behind on brown horse; Cornwallis 

himself was not present. French officers are on left. 
40

this day by Admiral Graves, that we may pass the bar by the

12th of October, if the winds permit, and no unforeseen accident happens: this however is subject to disappointment ...35

Washington wasted no time in relaying this intelligence to Admiral de Grasse. When Clinton and the British fleet finally arrived at 

the end of October, he found the French alerted to his activities and 

learned that Cornwallis had already surrendered. The fleet returned 

to New York without engaging de Grasse.

Diplomatic Communications Conclude the War

The surrender at Yorktown signaled the beginning of the end of 

British control in America, but intelligence continued to play a role 

throughout the remainder of the war. American representatives in 

Europe expressed the necessity for secret communications and used 

a wide variety of encryption systems to accomplish it.

Because so many people during the American Revolution created their own systems for correspondence with specific individuals, a multitude of different codes and ciphers were constantly in

use. Each system differed from the others in the key that was used.

Cipher keys and code lists needed to be accurately copied and

transmitted to the various receivers prior to messages being sent

in that system. This variety could be quite confusing and required

that multiple systems be held by each person. However, it was also

quite necessary. It was common practice for European governments

to have “Black Chambers” that opened and read other countries’

diplomatic mail.

“Whenever you write to me,” John Jay, the minister to Spain,

wrote to a Philadelphia businessman in 1781,“recollect that your letters will, in nine instances out of ten, be inspected before they reach 

me; write nothing, therefore, that you would wish concealed.”

36 He 

then described a code using Entick’s Spelling Dictionary. Rather than 

using the page-column-word count method, he recommended that 

20 be added to the page number and 10 to the word. To indicate in 

which of the two columns the word was located, he put a dot over the 

42

alphabetic order on the other side. The users randomly wrote in

the words next to the numbers to create their own code. The corresponding numbers were written on the opposite side next to the

words.39 

A Dutchman’s Cipher

In addition to the wide use of code lists, the diplomats also 

favored a cipher Charles Dumas created early in the war. 

Dumas, a German-born scholar, struck up a friendship and correspondence with Ben Franklin while Franklin served as an American representative in London (1757–1775). At the time of the Revolution, Dumas was in Holland. At Franklin’s suggestion, the United 

States made Dumas an agent. He was paid £100 and given secret 

assignments. He was to report on foreign diplomats in Holland, disseminate propaganda favorable to America, and win Dutch support 

for American war maneuvers.

Well aware of European Black Chambers, Dumas understood

the need for encryption. He created his cipher from a paragraph

of French prose. Each letter and punctuation mark was numbered

in a one-up order. For example, the first word of the paragraph

was Voulez-vous. V was numbered 1, O became 2, U was 3, and so

on.

He then wrote out a two-part sheet. One page listed each letter 

and symbol followed by all the possible number choices to represent 

that character. The second page listed each number and its corresponding letter or symbol.40 The French paragraph was 682 characters long, providing several options for the most commonly used 

letters. The letter E, for example, could be replaced by any one of 127 

different numbers.

James Lovell’s System

Less popular, but often used, was a keyword cipher created by 

James Lovell in the Committee of Foreign Affairs. He liked systems 

that could be committed to memory because they provided more 

44

Using Jefferson as the keyword in this example, the three alphabets created begin with J, E, and F.

1 J E F

2 K F G

3 L G H

4 M H I

5 N I J

6 O J K

7 P K L

8 Q L M

9 R M N

10 S N O

11 T O P

12 U P Q

13 V Q R

14 W R S

15 X S T

16 Y T U

17 Z U V

18 & V W

19 A W X

20 B X Y

21 C Y Z

22 D Z &

23 E & A

24 F A B

25 G B C

26 H C D

27 I D E

To cipher a word, such as Fleet, the user simply moves down 

the columns, finding each letter and writing down the corresponding 
45

number. F in the column under J in the keyword corresponds to 24.

The second letter is found in the second column and its number is 

noted: L in the column under E is 8.The process continues, rotating 

through columns, until the message is complete. Fleet becomes 24, 8,

27, 23, 16.

However, the system didn’t always work as well as it could have. 

One problem came from the way Lovell sent the keyword.For example, in a message to John Adams, Lovell suggested the keyword this 

way: “You certainly can recollect the name of that family where you 

and I spent our last evening together with your lady before we sat out 

on our journey hither. Make regular alphabets in number equal to the 

first sixth part of that family name.”

41

In a letter to Robert Livingston, the Secretary of Foreign Affairs,

Adams complained: “I know very well the name of the family where 

I spent the evening with my worthy friend Mr. ___ before we set off, 

and have made my alphabet accordingly; but I am on this occasion,

as on all others hitherto, unable to comprehend the sense of the passages in cypher.”

42

Another diplomat and member of the Continental Congress,

Francis Dana, on one occasion found Lovell’s message unintelligible 

because he could not remember “the name of the family in Charlestown, whose nephew rode in company with you from this city to 

Boston.”

43

Because Lovell encrypted official communications from the Continental Congress to its delegates abroad, the members of the Peace

Commission in Paris received their instructions in Lovell’s cipher. 

John Adams, who, as always, had trouble deciphering the Lovell 

cipher, didn’t read an important part of the letter. The instructions 

included the recommendation that the committee follow the direction of France. He even accused Benjamin Franklin of intentionally 

withholding the information from him. It wasn’t an instruction he 

was inclined to follow anyway.

44 In the end, the committee, particularly John Adams and John Jay, negotiated with the British representative without consulting the French.
46

In November 1782, the British and Americans signed the preliminary treaty without the knowledge of the French.The final Treaty of Paris, signed in September 1783, officially ended the Revolutionary War in America and established the United States as a free, 

independent, and self-governing country.

On November 25, 1783, the British evacuated New York. George 

Washington victoriously entered the city right behind them. The 

Americans were finally in possession of New York City, and the War 

for Independence was over. 

Conclusion

Hard-fought independence from Britain was achieved with the 

help of codes, ciphers, invisible ink, visual communications, and hidden messages. These techniques protected information traveling 

between the United States and its representatives in Europe. They 

also helped George Washington decisively plan his strategy. Spies,

Signing of Preliminary Peace Treaty in Paris, November 30, 

1782. Painting by C. Seiler, Library of Congress
47

like those in the Culper spy ring in New York, used various methods 

to keep him abreast of British movements, supplies, and intentions.

Because of the spies’ efforts, Washington learned of British spies 

in his midst as well as British plans against American and French 

forces. With this foreknowledge he was able to successfully protect 

the French fleet’s arrival in Newport and make his move against 

Yorktown.

Unfortunately, secrets couldn’t always be protected from trusted

men who also served the British. Men like Dr. Benjamin Church and

Benedict Arnold supplied the British commanders with important

details of the American intentions. Church used a simple cipher to

inform General Gage of patriot supplies and plans. Arnold used a dictionary code to tell the British of Washington’s movements as well as

propose the sale of a major, strategic American stronghold,West Point.

The British too, used similar methods to communicate their own

secrets. Hiding messages behind masks or inside ordinary objects was

a common way to protect their information. However, long practiced

in the arts of encryption, they used other techniques to a great extent.

Loyalist Benjamin Thompson used invisible ink to provide details of

rebel intentions very early in the war, while Cornwallis used ciphers to

relay his situation at Yorktown near the end of the war.

Reading some of the intercepted messages of the British gave 

the Americans vital information. Understanding encrypted messages 

between British generals Clinton and Cornwallis helped confirm and 

solidify Washington’s plan at Yorktown.

 Although the war was not won or lost based on any one secret,

the secrets of the revolution—those kept and those revealed—played 

a role in changing the world.

Jennifer Wilcox is museum administrator and educational coordinator of the National Cryptologic Museum,

Ft. Meade, MD.
48

Notes

1. David Kahn, The Codebreakers (New York: Macmillan, 1967), 138.

2. Benjamin Thompson, “Letter to ? 6 May 1775,” Spy Letters of the 

American Revolution, in the Sir Henry Clinton Collection of the 

Clements Library, University of Michigan. http://www2.si.umich.

edu/spies/index-gallery.html.

3. Kahn, Codebreakers, 180.

4. Thompson, Spy Letters.

5. John Bakeless, Turncoats, Traitors, and Heroes. (Philadelphia: Lippincott, 1959), 36.

6. S. Tomokiyo, “Benjamin Church and the Cipher Letter,” First 

Codebreaking in the American Revolution, 2009, http://www.

h4.dion.ne.jp/~room4me/america/code/church.htm.

7. Kahn, Codebreakers, 175–176.

8. William Howe, “Letter to John Burgoyne, 17 July 1777,” Spy 

Letters.

9. Ibid.“Henry Clinton to Burgoyne, 10 Aug 1777.”

10. Ibid.

11. “Intelligence Techniques,” Intelligence in the War of Independence

(Washington, DC: Public Affairs, Central Intelligence Agency, 

1997), 30.

12. George Washington, “Letter to Benjamin Tallmadge, 5 Feb 

1780,” George Washington Papers at the Library of Congress, http://

memory.loc.gov/mss/mgw/mgw4/064/0200/0226.jpg.

13. Benjamin Tallmadge, “Talmadge, 1783, Codes,” Washington 

Papers http://memory.loc.gov/mss/mgw/mgw4/094/0000/0022.

jpg.

14. Samuel Culper Jr., “Letter to John Bolton, 6 Aug 1779,”Washington 

Papers http://memory.loc.gov/mss/mgw/mgw4/060/0800/0873.

jpg.

15. Samuel Culper, “Letter to John Bolton, 12 Nov 1780,” [Benjamin 

Tallmadge] Washington Papers http://memory.loc.gov/mss/mgw/

mgw4/072/0700/0704.jpg.

16. George Washington, “Letter to Benjamin Tallmadge, 5 Feb 

1780,” Washington Papers http://memory.loc.gov/mss/mgw/

mgw4/064/022/0226.jpg.

17. Samuel Culper, “Letter to Benjamin Tallmadge, 15 July 

1779,” Washington Papers http://memory.loc.gov/mss/mgw/

mgw4/060/100/0178.jpg.
49

18. Carl Van Doren, Secret History of the American Revolution (New 

York: Viking, 1941), 362; quotes British chief justice Smith as saying Clinton told him he had learned about the fleet from Arnold.

19. Ibid., 271, citing B. F. Steven’s Facsimile of the European Archives,

730.

20.Samuel Culper, “Letter to Richard Floyd,20 July 1780,”Washington Papers; http://memory.loc.gov/mss/mgw/mgw4/068/0400/

0422.jpg.

21. Samuel Culper, “Letter to Caleb Brewster, 20 July 1780,”Washington Papers; http://memory.loc.gov/mss/mgw/mgw4/068/0400/

0421.jpg.

22. Morton Pennypacker, General Washington’s Spies on Long Island 

and in New York (Brooklyn, NY: Long Island Historical Society, 

1939), 87, uses an uncited report from Clinton to Lord Germain.

See also Alexander Rose, who cites B. F. Steven’s Facsimile, vol. 

7, no. 730, as having a similar letter addressed to William Eden,

chief of British intelligence.

23. Benedict Arnold,“Letter to John Andre, 15 July 1780,” Spy Letters, http://www2.si.umich.edu/spies/index-gallery.html.

24. £20,000 was then equivalent to more than $31,000. According to a 

conversion website, £20,000 from 1780 would be worth more than 

£2,130,000 today, which equates to more than $3,375,000. http://

www.measuringworth.com/calculators/ppoweruk/ and http://

coinmill.com/GBP_USD.html.

25. Benedict Arnold,“Letter to ‘John Anderson’ (John L. Andre), 30 

Aug 1780,” Washington Papers, http://memory.loc.gov/mss/mgw/

mgw4/070/0100/0184.jpg.

26. Van Doren, Secret History, 298.

27. Charles Cornwallis, An Answer to that part of the Narrative of

Lieutenant-General Sir Henry Clinton, K.B. which relates to the conduct of Lieutenant-General Earl Cornwallis During the Campaign 

in North America in the year 1781 (London, 1783), 174; Google 

Books, 2011.

28. Ibid., 173–174.

29. Charles Cornwallis, “Letter to Henry Clinton, 8 Sep 1781,”

Washington Papers, http://memory.loc.gov/mss/mgw/mgw4.080/

1000/1035.jpg. 

30. Ibid. For decryption, see also Cornwallis, An Answer, 192.

31. James Lovell,“Letter to Nathanael Greene, 21 Sep 1781,”in Letters of Members of the Continental Congress. Ed. Edmund C. Bur-
50

nett (Washington, DC: Carnegie Institute of Washington, 1933),

vol. 6, 224.

32. George Washington,“Letter to James Lovell, 6 Oct 1781,”Washington Papers, http://memory.loc.gov/mss/mgw/mgw4/081/0300/

0391.jpg.

33. Charles Cornwallis, “Letters to Sir Henry Clinton, 11 and 15 

Oct 1781,”An Answer, 204.

34. Ibid., 204–205.

35. Sir Henry Clinton,“Letter to Charles Cornwallis 30 Sept 1781,”

An Answer, 202–203.

36. John Jay, “Letter to William Bingham, 8 September 1781,” http://

www.familytales.org.

37. Ibid.

38. John Jay, “Letter to Robert Morris, 19 November 1780,” http://

www.familytales.org.

39. Kahn, Codebreakers, 184.

40. Charles W. F. Dumas,“Cipher,”Continental Congress–Papers, U.S. 

National Archives and Records Administration (NARA), 2006.

http://www.footnote.com/image/#172689.

41. Ralph E. Weber, United States Diplomatic Codes and Ciphers:

1775–1938 (Chicago: Precedent, 1979), citing Burnett’s Letters of

the Members of the Continental Congress, vol. VI, 125.

42. John Adams, “Letter to Robert Livingston, 21 Feb 1782,”

Continental Congress–Papers, http://www.footnote.com/image/

#436097.

43. Weber, Diplomatic Codes, 33, cites this quote in a letter from 

James Lovell to Francis Dana dated 6 January 1781 in the papers 

of John Adams. This author was unable to verify that letter. A 

later letter states that Dana could not decipher the letter because 

“I cannot recollect the person whose family name is alluded to.”

Francis Dana, “Letter to John Adams, 16 Mar 1781.” Founding Families: Digital Editions of the Papers of the Winthrops and 

the Adamses, 2007, http://www.masshist.org/publications/apde/

portia.php?id=PJA11d175.

44. Gregg Lint and William Hay, “The Men Who Signed the Treaty 

of Paris,” in presentation for The National Archives Experience, 

3 Oct 2008, 5, 17. See also Weber, Diplomatic Codes, 31.
51

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