German Cipher Machines 

of World War II
Cover Photo:

German soldiers using the Enigma in the field.
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German Cipher Machines

of World War II

David P. Mowry

Center for Cryptologic History

National Security Agency

2003
1

Introduction

Along with breaking the Japanese diplomatic cryptosystem, usually referred to as PURPLE, probably the

greatest example of Allied cryptanalytic success in World War

II was the breaking of the German Enigma machine. This

cryptodevice was used by all of the German armed forces as

the primary cryptosystem for all units below Army level or

the equivalent. As D-Day approached, other German cryptodevices, the SZ-42 and the various T-52 machines, assumed

great importance since they were used by the higher

commands of the German armed forces. Many references to

these German machines in the histories fail to provide

information on what they looked like or how they worked.

Another group of cryptodevices, those invented by Fritz

Menzer for the Abwehr (Counterintelligence), have received

little or no notice in the literature and are unknown to the

public. This brochure is an attempt to remedy both lacks.

The author is deeply indebted to Mr. Ralph Erskine of

Belfast, U.K., for the information he has provided concerning

Fritz Menzers Schluesselgeraet 39 (SG-39).

Enigma

In 1925 the German Army purchased several examples of

a commercially produced cipher machine called the

Enigma, manufactured first by Chiffriermaschinen

Aktiengesellschaft, a company owned by Arthur Scherbius,

and later by Chiffriermaschinen Gesellschaft Heimsoeth und

Rinke. After some modification, the Army adopted the

machine for extensive use.1

Example of a wiring maze
2

The standard military Enigma used three 26-point wired

metal and black plastic rotors selected from a set of five to

eight. Each rotor was a cylinder with a large, moveable

notched wheel on one end with an alphabet (or numbers)

around its circumference. One face of the cylinder had

twenty-six spring-loaded copper pins protruding from it and

the other face had twenty-six flush copper contacts. (See

figures 3 and 4.) Inside each cylinder was a wired maze

connecting the contacts to the pins.

Sample Enigma Encryption (without Stecker).

A plaintext R would, in this case, 

produce the cipher value Q.
3

With this rotor, the letters ROOSEVELT would come

out as SMMGZCZDT. Not too difficult to read just

monoalphabetic substitution. But Enigma used three rotors,

each one wired differently, and a reflector. When a letter was

input, the rightmost wheel would turn one space forward and

an electrical pulse would route, through each wheel in turn,

then through the reflector, then back through the three

Fig. 1. The Enigma in use
4

wheels by a different route and a glow-lamp would light to

show the encrypted character. When the notch on that wheel

progressed around to the reading point, the middle wheel

would advance one space; and when the notch on the middle

wheel progressed to its reading point, the leftmost wheel

would advance one space. It would take 16,900 characters to

return the three wheels to their initial position. By limiting

allowable message length, this cycling would not happen.

Figure 2 shows a standard military Enigma in its wooden

carrying case. All of its essential elements except the rotors

(shown on page 5) are visible. From top to bottom: on the

open lid: spare bulbs, a dark green screen for covering the

lights at night, instructions on operating and caring for the

machine, and spare plugs for the plugboard; and the body of

the machine with the three rotors covered, the power source

dial, the output letter panel, the input keyboard, and the

plugboard or stecker.

Fig. 2. Standard

military Enigma
5

The following description of the Enigma setup procedure

is taken from the National Cryptologic Museum brochure

Solving the Enigma: History of the Cryptanalytic Bombe, by

Jennifer E. Wilcox. It took two and sometimes three people to

operate the machine, but first it had to be set up. This

involved selecting three rotors from the provided set

according to the instructions in the monthly key list. Each

rotor had a moveable placement notch found on an outer

ring. The notch

forced the rotor to

its left to step one

place forward and

could be moved to

a different point

on the rotor by

rotating the outer

ring (fig. 3). The

three rotors were

then assembled on

an axle in the

proper order (fig. 4)

and placed in the

machine (fig. 5).

Fig. 4. Assembling

the rotor set

Fig. 5. Putting the rotors 

in the basket

Fig. 3. Setting the notch ring
6

In addition, the stecker had to be applied. This was a

military addition to the original Enigma and consisted of a

plugboard with contacts for the letters of the alphabet. In

accordance with the key list, plugs were inserted into this

board in pairs to further encipher the characters. In figure 6,

for example, entering the letter Q on the keyboard would

result in the letter Y being introduced into the maze, and,

conversely, an encryption that would have lit the letter Y on

the display would now, after passing through the stecker,

light up the letter Q.

After the machine was set up, it was ready for use. The

wheels were set with three letters (or numbers) appearing in

the window as determined by the code clerk (fig. 7). These

Fig. 6. The stecker

Fig. 7.

Setting the

windows
7

were changed with each message sent, and the setting was

included at a prearranged point in the message indicator.

Encryption could then start. One operator used the keyboard

while either reading the message or having it read to him.

Another operator wrote down the cipher values as they lit up

on the display (fig. 1). The recipient would set the rotors

according to the transmitted window setting and decipher the

message. Encryption and decryption followed the same

procedure. 

The FISH Machines

Under the general name of Geheimschreiber (Secret

writer), the Germans used two devices for enciphering highlevel (Army level and above) radioprinter communications.

(Enigma was used for Army level and below.) These were the

T type 52B/C/D/E, built by Siemens & Halske, and the SZ40/SZ-42, built by Standard Elektrik Lorenz. The SZ

meant Schluesselzusatz (key attachment), so-called because

the essential encryption mechanism was in a box that could

be detached from the radioprinter machine. The British

referred to these machines by the generic name of FISH

and specifically as STURGEON and TUNNY, respectively.

The British titles will be used in this paper, inasmuch as these

are the more familiar names.

General Comments on Enciphered Radioprinter

Baudot Code

Radioprinter communications are based on the Baudot

code, which replaces each letter with five electrical impulses

(or bauds), represented here by + (or mark) and o (or

space). There are thirty-two such combinations possible

(25 = 32), accounting for twenty-six letters plus six extra

characters. These six extra characters will be represented
8

here by 3, 4, 8, 9, +, and /. The complete Baudot code is

shown below.

Radioprinter Operation

When a radioprinter key is struck, a sequence of seven

impulses is generated and transmitted to the receiving

radioprinter one at a time, in order. The first of these is the

start pulse, which alerts the receiving radioprinter to

receive the next six impulses. Five of these are the Baudot

coding of the letter typed, causing the receiver to print that

letter. The last impulse is the stop pulse.

Encipherment of the radioprinter signal is accomplished

through baud addition in that the plaintext bauds are

combined with key bauds according to the rule:

| + o

+ | o +

o | + o

Thus, 

+ and + combine to give o These rules can be condensed by saying that like

+ and o combine to give + signs combine to give o, and unlike signs combine

o and + combine to give + to give +.

o and o combine to give o

It follows that the stream for plain D: + + o o + o +

Enciphered with the encryption stream: o + + o +

Gives the cipher text 8: + + + + + +

Likewise, the stream for plain U: + + + + o o +

Enciphered with the encryption stream: + o + + +

Gives the cipher text G: + o + o + + +

Start and Stop Beads

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 3 4 8 9 + /

+ + 0 + + + 0 0 0 + + 0 0 0 0 0 + 0 + 0 + 0 + + + + 0 0 + 0 + 0

+ 0 + 0 0 0 + 0 + + + + 0 0 0 + + + 0 0 + + + 0 0 0 0 + + 0 + 0

0 0 + 0 0 + 0 + + 0 + 0 + + 0 + + 0 + 0 + + 0 + + 0 0 0 + + 0 0

0 + + + 0 + + 0 0 + + 0 + + + 0 0 + 0 0 0 + 0 + 0 0 + 0 + 0 0 0

0 + 0 0 0 0 + + 0 0 0 + + 0 + + + 0 0 + 0 + + + + + 0 0 + 0 + 0
9

When a cipher unit is added to a radioprinter, there are

two types of operation that may be used. In on-line

operation, the plain text is typed and is immediately

enciphered by the machine, which transmits the cipher letter

instead of the plain letter. In off-line operation, the cipher

text is printed or, more likely, punched onto a paper tape for

later transmission.

When on-line operation is used, the cipher is not in

general broken up into message-length chunks so that several

messages might be sent in succession without resetting the

cipher unit for each one and thus possibly causing the two

terminals to go out of synchronization.

Description of the TUNNY System

The name TUNNY referred specifically to a device

attached to a Lorenz teletypewriter to encrypt its

output (figs. 8-10). Operation was as follows: The

Schluesselkasten or cipher box consisted of twelve wheels,

each with a prime number of settable lugs (sprossen) around

Fig. 8. TUNNY teletype base, in safe
10

the circumference (wheel lengths were not prime). Each

wheel was driven from a common shaft through a pair of

gears. 

Fig. 9. TUNNY rotor basket

Fig.10. TUNNY rotors
11

For purposes of description, the wheels are numbered 1 to

12 reading from left to right from the front of the box (fig. 10).

Baud-by-baud encipherment was accomplished by adding

the plain baud to the mark or space appearing on the

enciphering wheels.The periodic, or so-called c(chi) wheels

(Numbers 1 to 5), are of lengths 41, 31, 29, 26, and 23 and step

once with each character enciphered. The aperiodic, or y(psi)

wheels (Numbers 8-12) are of lengths 43, 47, 51, 53, and 59.

The first c wheel (number 1) interacts with the first y wheel

(number 8) forming a combined impulse which acts on the

first impulse of the plaintext letter being enciphered.

Likewise, the 2 and 9, 3 and 10, 4 and 11, and 5 and 12 wheels

interact with the respective plaintext impulses. Wheels 6 and

7 were control wheels that caused irregular motion in the

encipherment wheels.

The primary motor wheel or m1 (mu1) (Number 6), of

length 61, controls the motion of the secondary motor, or 37

wheel (m2) (Number 7), which in turn controls the motion of

the aperiodic wheels. A mark in the number 6 wheel compels

motion of the number 7 wheel; after this motion, if a mark is

at the reading position of the number 7 wheel, it compels

motion of all the y wheels. Conversely, a space in the number

6 wheel denies motion to the number 7 wheel, and a space in

the number 7 wheel denies motion to the five y wheels. As

used by the Germans, the number 6 wheel had between

eleven and nineteen spaces. The number 7 wheel consistently

had eleven spaces. Two consecutive spaces were very rare in

either wheel.

In addition, there is a secondary c effect on the y wheels.

That is, a space in the second c wheel (number 2) two

positions in back of its active position compels motion of the

y wheels. When the second c was used in conjunction with the

motor, the number 7 wheel had sixteen spaces, resulting in

the same proportion of spaces to marks as when no

secondary c wheel effect was used. The patterns of the c and

y wheels were changed monthly, the m wheel patterns daily. 
12

Here is a sample run of fifty characters showing the effect

of the above with the exception of the secondary c effect.

Arrows and underlined bauds show where each wheel

completes its cycle and starts over.

y m1 m2 P C

12345 12345

1 +oo+o +o+oo o + T M

2 +oooo +oooo + + H H

3 o++o+ o+o+o o o E X

4 +++oo o+o++ + + 9 X

5 oooo+ +oooo o o Q I

6 +o+o+ ++ooo + o U W

7 oo+oo oo++o + + I A

8 +o+oo oooo+ o + C G

9 oo+o+ oo+oo + o K Q

10 +oooo ++o+o + + 9 Y

11 o+o+o o++oo + + B A

12 o++oo oo+++ + o R 3

13 +o++o oo+oo o + O V

14 +o++o o+++o + + W Y

15 oo+oo oo+o+ + o N A

16 oooo+ +oooo + + 9 L

17 +oooo +oooo + + F T

18 +oo+o oo+oo + o O F

19 +oo+o ooo++ + + X T

20 +o+o+ +o++o + + 9 8

21 oo+oo oo+oo o o J E

22 +oo++ oooo+ + + U R

23 ++ooo oo+o+ + + M V

24 o++oo +oooo + o P Z

25 oo+oo oo+oo + + E 9

26 oo+o+ oo++o + + D B

27 ++o+o ++ooo o + 9 Q
13

28 +ooo+ o++++ + o O Z

29 oo+o+ ++ooo + + V L

30 +oooo ++o+o + + E F

31 +oooo ooo++ + + R K

32 +o+o+ oo+oo + o 9 Y

33 oo+oo oooo+ + + T 9

34 o+ooo o+o+o o + H A

35 o++oo o++oo + + E P

36 +o+oo +oo++ + o 9 S

37 +o++o ++ooo + + L 5

38 oo+o+ o+oo+ + + A J

39 ooo+o oo+oo + + Z R

40 ooo+o o++o+ o o Y A

41 oo+oo ooo++ + + 9 Y

42 +++oo o+oo+ + o D T

43 +++o+ o++oo + o O N

44 oo+++ ++++o + + G X

45 +oo+o +oooo + + S 9

46 oooo+ oo+oo + o 9 M

47 +oooo o+oo+ + + B M

48 ooo+o +oooo o + A 5

49 +o+oo +++oo + o C Z

50 oo +++ oo+o o + + K F
14

Description of the Sturgeon System

There is a superficial resemblance between the TUNNY

and STURGEON machines in that each has a basket

containing large rotors. (See figs. 10 and 11.) However, the

TUNNY basket is attached to a Lorenz radioprinter machine

while the STURGEON basket is an integral part of the

Siemens-Halske T52 equipment. Also, the philosophy and

operation of the two machines are completely different.

Where TUNNY performs a substitution for each plaintext

letter through baud addition using wheels 1-5 and 8-12,

STURGEON performs a substitution for each plaintext letter

through baud addition using wheels 1-5 and then transposes

the bauds in the resulting cipher letter using wheels 6-10.

(There are no motion wheels.) In other words, there is a tenlevel key stream.

Production of this ten-level key stream can be

accomplished by four slightly different methods, giving rise

to four STURGEON models: T-52-B, T-52-C, T-52-D, and T52-E. (T-52-A was an experimental model that was never

Fig. 11. Sturgeon
15

used.) There are ten wheels in each model, and each wheel

has a fixed notch pattern cut into its perimeter. The notches

are referred to as o and the raised portions as +. The

wheels have lengths (+s + os) of 73, 71, 69, 67, 65, 64, 61,

59, 53, and 47, reading from 1 to 10.

The different key productions are obtained from different

uses of the notch patterns and from different ways of

controlling the stepping of the wheels. For each wheel there

is an encipherment reading station, which reads the baud

(+ or o) from the wheel at a given enciphering position. These

ten reading stations may be arbitrarily steckered (plugged) to

ten points labeled 1, 3, 5, 7, 9, 2, 4, 6, 8, and 0. The notch

patterns may be used with either a 1 to 1 stecker or a 4 to

1 stecker, and the stepping may be either regular or

irregular. The models may be described on the basis of

stecker and stepping as follows:

On a 1-1 stecker, the substitution keys come from the

points 2, 4, 6, 8, and 0, while the transposition keys come

from the points 1, 3, 5, 7, and 9. In this case, each baud of the

key stream comes from a single wheel and is called a singlewheel stream.

On a 4-1 stecker, each key element is formed by the sum

of four points, as:

Substitution Transposition

Baud 1 = 5+7+4+8 Baud 1 = 1+3+6+0

Baud 2 = 3+5+9+0 Baud 2 = 2+4+6+8

Baud 3 = 1+3+2+8 Baud 3 = 5+7+6+0

stecker

1-1 4-1

+--------+----------+

| T-52-B | T-52-C | regular

+--------+----------+ stepping

| T-52-D | T-52-E | irregular

+--------+----------+ 
16

Baud 4 = 9+2+6+0 Baud 4 = 1+3+5+4

Baud 5 = 7+9+2+8 Baud 5 = 1+7+9+4

For example, the first baud of the substitution stream is

obtained by adding (using the usual rules) the bauds that are

read from whichever four wheels happen to be steckered to

points 5, 7, 4, and 8. In this case each level of the key-stream

is a four-wheel stream.

After the plain letter has thus been enciphered, its bauds

are transposed. If the first baud on wheel 6 is a o, bauds 1

and 5 of the cipher character are swapped; a o on wheel 7

swaps bauds 4 and 5; a o on wheel 8 swaps bauds 3 and 4;

an o on wheel 9 swaps bauds 2 and 3; and a o on wheel 10

swaps bauds 1 and 2. A + in any of these positions would

result in that specific transposition not being performed.

The term regular stepping (or regular motion) means

that each wheel moves one position after each encipherment.

Irregular stepping means that the wheels do not all advance

after each encipherment. In fact, the stepping of each wheel

is controlled by some of the other wheels. This is effected by

placing a motion reading station on each wheel, and

arranging definite rules by which the signs read on one wheel

help determine whether another wheel steps or stands still

after a particular encipherment.

There are two categories of irregular motion, Ohne

Klartextfunktion and Mit Klartextfunktion (without

plaintext function and with plaintext function). The rules are

shown below.

OHNE

1, 2, 3, & 4 step 1 if 5 = o or 6 = o

5 steps 1 if 6 = + or 7 = o

6 " 1 if 7 = + or 8 = +

7 " 1 if 8 = o or 9 = o

8 " 1 if 9 = + or 10 = o

9 " 1 if 10 = + or 1 = o

10 " 1 if 4 = o or 5 = 
17

A wheel stands still (sticks) if neither of its motor wheels

forces it to move. All signs are read from the motion reading

station.

P3 refers to the third baud of the plaintext in the previous

wheel position, not the present one. Note that in OHNE

motion, the wheels 1, 2, 3, and 4 either all move or all stick.

The reason for this is that it guarantees a cycle of at least

73x71x69x67, or 23,961,009. With MIT no cycle guarantee is

necessary. Note also that MIT motion is a form of autokey,

with the plaintext contributing to the key.

The Menzer Devices

Fritz Menzer

Ostwin Fritz Menzer was born 6 April 1908 in the village

of Herrndorf in Saxony. At the age of eighteen he enlisted in

the Army as a mechanic and was assigned to a motor

battalion in Leipzig. Having shown an aptitude for

cryptanalysis, in May 1935 he was transferred to OKW/Chi

(the Armys cryptologic bureau), where he received his first

formal training in the field. His enlistment expired on 31 May

1938, and he continued to work as a civilian. Two years later,

he was promoted to the rank of superior government

inspector. In 1942 Admiral Canaris, the chief of the Abwehr,

charged Menzer with testing the security of Abwehr

MIT

1 steps 1 if 2 = + or 3 = + or P3 = +

2 steps 1 if 3 = o or 4 = + or P3 = +

3 steps 1 if 4 = o or 5 = + 

4 steps 1 if 5 = o or 6 = o

5 steps 1 if 6 = + or 7 = o or P3 = o

6 steps 1 if 7 = + or 8 = + or P3 = o

7 steps 1 if 8 = o or 9 = o 

8 steps 1 if 9 = + or 10 = o

9 steps 1 if 10 = + or 1 = o 

10 steps 1 if 1 = + or 2 = o
cryptosystems. From then to the end of the war, Menzer

worked for the Abwehr as technical consultant in

cryptography.2

During Menzers service with OKW/Chi and the Abwehr

(1935-1945), he was responsible for a number of advances

in the science of machine cryptography. In general, his

procedure was to adapt the use of Hagelin pin wheels to

provide for irregular wheel motion in cryptoequipment.

The two major types of crypto-equipment used by the

Germans before World War II were the Enigma and

machines made under the Hagelin patents. As we have seen,

in the Enigma motion was odometer-type, with the only

variation being the starting point of the cycle on each rotor.

In the Hagelin machines, as you will see, the key wheels also

stepped once with each encipherment. Menzers inventions

were designed to make such motions unpredictable.

The Hagelin Patents

Boris Caesar Wilhelm Hagelin was a Swede born in 1892

in the Caucasus, probably in present-day Georgia. He

received his degree in mechanical engineering from the Royal

Institute of Technology in Stockholm in 1914. After gaining

engineering experience in both Sweden and the United

States, he returned to Sweden in 1922. At that time his father,

a stockholder in Aktiebolaget Cryptograph (Cryptograph,

Inc.), placed Boris in that firm to represent the family

investment. In 1927 the firm was reorganized as Aktiebolaget

Cryptoteknik with Boris in charge. The first crypto-machine

using what would be known as Hagelin action was the C-36,

which, with modifications, was adopted by the U.S. Army as

the Converter M-209. The M-209 was used in military units

division level and below during WWII and into the Korean

War. The description of the workings of the M-209 given here

was typical of the action now known as Hagelin action.

The following description of Hagelin action in the M-209

is keyed to the photograph in Figure 12. The M-209 was

18
essentially a Hagelin C-36 device made under license in the

United States for use by the American armed forces in World

War II.

There are six key wheels (1) whose lengths are mutually

prime. These lengths are indicated by different lengths of

letter sequences (26, 25, 23, 21, 19, and 17) on the wheels.

Each key wheel steps once with each encipherment,

returning to its starting position after its period. These wheel

lengths give a cycle length of 26x25x23x21x19x17 =

101,405,850.

19

Fig. 12. The M-209
On each key wheel there are pins corresponding to the

letters (5). Each pin can be set as active (i.e., pushed to the

left so it can engage a lug on the cage) or inactive.

The cage (3) is a cylinder composed of twenty-seven

bars bearing projections known as lugs (4), which are

positioned to correspond to the key wheels. The cage rotates

once with every encipherment. If a lug encounters an active

pin, the bar is slid to the left so that its end projects past the

end plate (2). In each case, this effectively creates a gear

tooth. These teeth engage another gear and turn it in

accordance with the total number of teeth projecting from

the cage. The number of lugs for each key wheel governs the

number of teeth and thus the kick for that wheel.

To set the device up for encryption, the pins and lugs must

be set according to a keylist giving the settings for the day.

The key wheels are then turned by hand to position six letters

in the starting window. These letters constitute the message

indicator, which must be included in the message in some

way to inform the decipherer where to set the wheels for

decryption.

In operation, the encipherer sets the machine to

encipher and turns a knurled knob (8) on the left side of the

machine to align the desired letter on the plaintext wheel (9)

with an index mark. A low-frequency letter such as X is

used as the word separator. The operating lever on the right

side of the machine (11) is then rotated. The cage rotates, the

gear is turned and turns the print wheel, which is fixed to the

plaintext wheel, the number of places determined by the

projecting teeth on the cage. A counter (10) keeps track of the

number of characters enciphered. 

With the completion of the movement of the operating

lever and its return to its normal position, the paper tape

advances one position, the print wheel prints the cipher

character on paper tape, the bars in the cage return to their

normal position, the key wheels step one position, and the

20
machine is ready for its next input. Cipher characters are

printed on gummed paper tape in five-letter groups.

The decipherer, in turn, sets his machine up in accordance

with the key list. When the message is received, he sets the

key wheels to the message indicator, sets the machine to

decipher and follows the same procedure as was used in

enciphering. The plain text is then printed on paper tape in a

continuous stream.

Schluesselgeraet 39 (SG-39)

In June 1945 Major Howard C. Barlow, USA, reported

to Colonel George A. Bicher concerning Menzers

Schluesselgeraet 39 (SG-39).3 He had flown to Frankfurtam-Main on 24 June to investigate the SG-39. In the course

of his investigation, he found that although invented in 1939,

only three of the machines had been constructed, and only

one of these was complete. According to one of the

technicians who worked on the machine, the long delay in

production was caused by the Armys inability to make up

their mind whether they wished this model to be capable of

operating on radioprinter lines or only for the production of

printed tape. The eventual plan was to make this machine for

use by lower-echelon units and later to make a similar

machine which was to replace the T52D and T52E

(STURGEON).4 

Of the three machines identified by Barlow, one was

complete, the second was missing the printing mechanism,

and the third lacked both the printing mechanism and the

rotor mechanism. The first two had been packed into boxes

and shipped to a military depot at Tauberbischofsheim on 22

March 1945. Barlow took the third, and most incomplete,

machine, but decided not to pick up the boxes containing the

completed machines at the Tauber-bischofsheim Depot as it

was felt to be too long a chance to be worthy of the 150-mile

trip. As a result, the following photographs are of a very

incomplete machine.

21
22

Fig. 14. Incomplete SG-39

Fig. 13. Incomplete SG-39
The SG-39, which was invented by Menzer in 1939, was an

electrical motor-driven cipher machine intended eventually

to replace the standard Enigma. The SG-39 had a standard

23

Fig. 16. SG-39 Layout

Fig. 15. SG-39 electrical circuits
typewriter keyboard; a three-position switch for Off,

Encipher, and Decipher; a counter; a dual-printing unit;

a motor-driven cipher maze; and changeable plugboards for

rotor input and re-entry points. A block diagram of the

electrical operation of the machine is given in figure 16, and

the general mechanical layout is shown in figure 17. One of

the dual printers printed the clear text and the other

simultaneously printed cipher text spaced into four- or fiveletter groups. The cipher maze consisted of four electrical

rotors, one of which was stationary, and three mechanical

wheels with the stepping of the electrical rotors being affected

both by Hagelin-type settable pins in the mechanical wheels,

and by further Hagelin-type settable pins contained as an

integral part of the electrical rotors setup on the equivalent of

the Enigma notch ring. Encipherment of a character through

the electrical maze was as is found in a normal Enigma.5

The stepping motions were as follows:

1. With each letter, the three mechanical wheels, which had

lengths of 21, 23, and 25, moved forward one position each. If

the pin setting of any mechanical wheel happened to be in an

active position, the corresponding rotor would move one step

forward. If, for example, the pins on wheels 1 and 3 were in

active positions and the pin on wheel 2 was not, then Rotor 2

would remain stationary and rotors 1 and 3 would step. Rotor

4 was used as a stator, that is, its position was set at the

beginning of the message and it remained stationary

throughout the message.

2. In addition to the stepping caused by the mechanical wheels,

there was an additional independent stepping motion caused by

the Hagelin-type pins on the periphery of each rotor. If the

Hagelin-type pin on Rotor 1 was in an active position, it caused

Rotor 2 to automatically move one step forward. If the pin on

Rotor 2 was in an active position, it caused both rotors 2 and 3

to move one step forward. If the pin on Rotor 3 was in an active

position, it caused Rotor 1 to move one step forward. Rotor 4

had no stepping motion. If a specific rotor had been given one

step forward by the mechanical wheels and in addition was

independently kicked one step by the pins on the electrical

rotors, only one of these kicks would take effect.

24
The SG-39 was fully automatic, in that when a letter key

was pressed, the plain and cipher letters were printed on

separate paper tapes, divided into four- or five-letter groups.

The outputted character was converted into five-level

radioprinter code before being fed to the print wheel. This

would have allowed the output to be used to punch five-level

paper tape for radioprinter transmission if so desired.

The cycle for an unmodified Enigma is 16,900. When set up

in accordance with Menzers instructions, the SG-39 had a

cycle length of 2.7x108 characters  more than 15,000 times as

long as the cycle length of the unmodified Enigma.

This mechanical cipher machine, invented in 1941, was

based on Hagelin encryption but included a mechanism for

variably stepping the Hagelin wheels.

The Schlüsselgerät 41 (SG-41) had six pin wheels which

were mutually prime. The first five of these wheels had kicks of

1, 2, 4, 8, and 10 active pins respectively. The sixth wheel made

these kicks positive or negative. Also, in addition to the pins

operating on the lugs, there was, for each wheel a motion

index reader, and, on the sixth wheel, a kick index reader.

The enciphering cycle (encryption of one letter) consisted of

three elements:

1. Step 1 took place if and only if the sixth wheel had an active pin

in the motion index position. If this were the case, then all of the

following occurred: Wheel 1 moved one step. Each of the

remaining four wheels moved one step unless the wheel to its left

had an active pin in the motion index position, in which case it

would move two steps.

2. A key kick was generated as in normal Hagelin action. If,

however, the sixth wheel had an active pin in the kick index

position, the key kick would be 25 minus the sum of all the other

kicks. In other words, under such a circumstance, the key would

complement itself.

3. This was identical to Step 1, except that it occurred whether or

not Wheel 6 had an active pin in the motion index position. In

this step, Wheel 6 also stepped one or two positions, depending on

the state of Wheel. 

6

25
The original specifications called for a lightweight,

durable machine to be used by units forward of division.

Menzer designed it to provide a cipher tape and to be

keyboard operated in order to improve the speed of

encryption. According to Menzers description, he was able to

redesign the arrangement of letters on the print wheels to

flatten the cipher frequency count as a result of the keyboard

operation.

Because of the wartime shortages of aluminum and

magnesium, the machine ended up weighing between

twenty-six and thirty-three pounds, too heavy for field use.

26

Fig. 17. Schlüsselgerät 41 ready for use
Removal of the keyboard would have lightened the machine,

but the redesign of the print wheels prevented their being

used directly for encipherment. Production stopped because

no one knew what to do. About 1,000 machines had been

constructed, and these were distributed to the Abwehr, which

began using them in 1944.7

Ease of maintenance was not a strong point of the SG-41.

Removal of the cover involved removing all external knobs

and cranks and then undoing six screws.

Schlüsselkasten

Although the Schlüsselkasten (Cipher Box) was not a

machine, it was intended to be a substitute or backup for

Enigma, and is therefore included in this paper. The

Schlüsselkasten was a mechanical cipher device making use

of the principle of sliding two printed strips against one

another according to a prescribed plan to generate the cipher

equivalents. The Germans intended to have 1,000 available

by October 1945 and to mass-produce 10,000 per month by

January 1946. It would have replaced the Enigma below the

level of division. Nineteen forty-five was too late; if it had

been introduced in 1942, it could have changed the course of

the war. Basically, the Schlüsselkasten was a twelve-ounce

aluminum box containing four Hagelin pin wheels and a coil

spring which determined the stepping of a sliding strip on the

top of the box.

Thirteen characters from each of two key-word mixed

alphabets* were written on the fixed base, and the other

thirteen of each on the top and bottom of the sliding strip.

The latter were so written that only one alphabet at a time

was in phase. Alphabets could be changed as often as desired.

In use, the slide was pulled to the right until it stopped,

winding the spring that drove the mechanism. Pressing a

button released the slide to move left. When at either or both

27

* The key-word mixed sequence in the figure is based on

Geheimschreiber and Frtizmenzer. 
28

Fig. 18. Schlüsselkasten

Fig. 19. Schlüsselkasten 41, rear view
of the reading positions A1 or A2, the pins on all four pin

wheels were all inactive, the slide stopped and encipherment

took place. If the step came from A1 alone or A1 and A2,

together, the slide took an additional step. When the slide

stopped, either the top or the bottom alphabet would be in

phase, and the cipher value could be read off. Pressing the

button again would allow the slide to slide left to its next stop.

Conclusion

The Germans had a good head start in the construction of

mechanical cryptodevices before the beginning of World War

II with Enigma, and developed excellent enciphered

teleprinter devices with the T-52s and SZ-40/SZ-42s. If

Menzers devices had been introduced in a timely manner

from 1940 on, they would certainly have complicated the

Allied cryptanalytic effort, which was strongly oriented

toward solution of Enigma traffic from 1939 on. This is not to

say that the Allies would not have been able to read German

traffic. The Germans did not intend to replace the Enigma on

higher echelon communications, and in the face of necessity,

methods would have been found to solve Menzers devices.

But the Allies would have lost the much of the edge that the

Poles presented to the British in 1939, when they turned over

the results of their analysis of the Enigma to GC&CS.

29
30

Fig. 21. Wooden mode-powered with elastic bands

demonstrated the rules of motion in this device. The disks,

T1-T4, represent slip-wheels which affect the relative

positioning of the four pin wheels, G1-04. The black and

white squares represent active and inactive pin wheels.

Dowels would be inserted into the holes corresponding to

positions where all holes were active or all inactive, and Z1

and Z2 would be pulled to the right and released. Each time

one of the four metal slips on Z2 encountered a dowel, the

mechanism would stop and a cipher value would be read off

of SK1 or SK3.

Fig. 20. These models, made by Fritz Menzer, were devised to

illustrate certain aspects of the working of the

Schlüsselkasten. No actual working models of this device are

available.
Notes

1. David Kahn, The Codebreakers (New York: The Macmillan Co.,

1967), 421-22.

2. David P. Mowry, Regierunge-Oberinspektor Fritz Menzer:

Cryptographic Inventor Extraordinaire, Cryptologic Quarterly, Vol. 2,

Nos. 3-4, Fall/Winter 1983-84, 21-36.

3. 79/49/TOPSEC/AS-14, TICOM DF-174, Description of Contacts

of Fritz Menzer with American and Soviet Authorities and Summary of

Career; WDGAS-14, European Axis Signal Intelligence in World War II

as Revealed by TICOM Investigations and by Other Prisoner of War

Interrogations and Captured Material, Principally German, Vol. 2.

4. TICOM I-53, Memorandum to Colonel George A. Bicher,

Investigation of Firm Telefonbau-Und-Normalzeit for Geraet 39, 27

June 1945.

5. Ibid.

6. Ibid.

7. WDGAS-14.

8. Report on SG-41 by Wilhelm Buggisch, 30 August 1945.

31