WASHINGTON 25, ~. d. 

CSGAS-14 22. September 1949 

MEMOHANDUM FOR: GENERAL CLARKE 

SUBJECT: Background of Policy in Regard to Making SIGABA Available 

t_o the British 

1. a. To begin with, it is important to note that when the 

ECM-SIGABA was conceived, the basic premise or requirement which 

the U. S. experts had to meet was this: a cryptographic machine 

for military use must be designed so that its capture or compromise 

will not jeopardize the security of future communications enciphered 

by that machine. The reason for this requirement is not only that 

research, development and testing of crypto-equipment is expensive 

and time-consuming, but also that during a war there is no time to 

repeat the research, development, testing, installing, and training 

of personnel each time a machine is lost, captured, or compromised. 

This requirement is certainly a logical one and the JroM-SIGABA fully 

met it when it was designed; it still meets the requirement despite 

the astonishing developments in the past 10 years in cryptanalytic 

machinery and techniques. All the top-level cryptologic technicians 

in both the Army and the Navy are absolutely sure that, in the 

present state of cryptanalytic technology, even if an enemy government with a good cryptanalytic organization had an :EDM-SIGABA, the 

reading of communications properly enciphered by that machine is 

impossible ,!fithout possession of the kf!Y' which gives the exact 

11 setting11 of the cr;rnto-elements for the day. In the minds of those 

technicians there never was and there still is no danger to U. s. 

communication security if the mach~ne is lost or compromised and 

hence there can be no loss in security of U. S. communications if 

the ECM-SIGABA were disclosed and released to the British. 

b. The problem as to whether the SIGABA should be disclosed 

and made available to the British is one which has confronted and been 

discussed by U. S. authorities ever since the 'equipment was introduced 

into service late in 1941. Although there was a high level decision 

to collaborate on cryptanalytic work, collaboration on cryptographic 

-work was much restricted. (See Incl. 1.) 

c. From the early days of our active participation in World 

War II, Combined conununications between U. S. Navy and British Navy 

over the North Atlantic convoy routes were very much hampered by the 

slowness and unreliability of the cryptosystem provided by the British. 

Declassified and appr?ved fo.r release by NSt: 2~ 99-26z170.1 _3. pursuant ~o~ ~~-0- 135.@,---._::, . .,., 
~F ID:A2435719 ~ 

CSGAS-14 !~? S~C~H 22 Sep 49 

SUBJECT: Background of Policy in R.egard to Making SIGABA Available to 

the British 

T~is consisted of a figure-code (British Naval Cypher No. 3) enciphered 

by additives. It was the only cryptosystem then available for Combined 

use. U. S. Navy technicians had some doubts as to the security of the 

system but these were minimized by the British. It was early in 1943 

that the U. S. Navy obtained proof that high convoy losses were 

attributable to German solution of the 11rit~sh system and German reading of convoy traffic. · 

d. In the early part of 1942 Colonel John H. Tiltman, officer 

in charge of the Services Division of the British cryptologic organization (GC & CS), came to Washington to discuas U.S.-British collaboration, 

including cryptographic systems for Combined U. S • .Army-British .Army 

{and RAF) communications. Authority was granted to discuss with him 

the possibility of using the strip cipher device and Converter M-209 

(Incl. 2). But the British did not think either of these suitable for 

the purpose. Though they had their TYPEX machine, they did not have 

enough of them for their own use, let alone enough to hand over to the 

U. S. for Combined communications. Besides, the U.S. experts did not 

think too highly of the TYPEX in comparison with the ECM-SIGABA and, 

furthermore, to adopt the TYPEX for Ca-ABINED communications would mean 

that each U. S. headquarters would have to carry .fil'!g large ma.chines. 

The Briti'sh knew we had a machine and were in heavy production. They 

therefore wanted the :&JM-SIGABA and brought heavy pressure to bear 

upon U. S. high level authorities to disclose it in the hope of getting 

it released to them to replace the TYPEX and make it unnecessary for them 

to carry :E!2 machines. Apparently the effort to gain.a~ least a look 

at the machine was successful because on 25 April 1942 verbal authority 

was granted to both ./rrmy and Navy representatives to show Col. Tiltman 

the machine. (Sea handwritten note at bottom of page 2 of Incl. 2.) 

A joint demonstration of the ECM-SIGABA was made in the Navy Department 

and the basic cryptographic principles were explained to Col. Tiltman. 

In return Col. Tiltman demonstrated the TYPEX machine to the Army 

representative, who had never seen it. 

e. British pressure to get the ECM-SIGABA released continued. 

It is my distinct recollection that the resistance was much stronger 

in the Army' than in the Navy at that time. This recollection is supported 

by a memorandum dated 9 July 1942 (Incl. 3) in which the President asked 

General Marshall to look into the matter of a more intimate exchange 

of information between the cipher experts of the U. S • .P:rmy and the 

British .Army, implying that such an exchange was in effect between 

those experts of the U. S. Navy and the British Navy. The mem~randum 

2 
CSGAS-14 

SUBJEJT: 

22 Sep 49 

Background of Policy in Regard to Making SIGABA Available 

to the British 

was referred to General George V. Strong, A.C. of S., G-2, who neatly 

side-stepped the issue. He was able to do this because the President's 

memorandum was not very clear and did not specif'ically mention the 

question of releasing the SIGABA. I am sure that this was the point 

at issue but I have no documents to support this part of my recollection. General Strong simply noted that "intimate exchange of technical 

cryptanalytic information ••• appears to be quite satisfactory to both 

sides 11 and that studies and coni'erences pertaining to an exchange of 

cryptographic information had been in progress for about three months 

and would soon be completed. 

f. The studies and conferences referred to above were those 

dealing with the development of the CCM. This was a compromise solution to the problem of a Combined machine and was a project largely 

initiated and completed by the U. S. Navy. However, before embarking 

on this project, U. S. Navy experts tried to convince higher Navy 

authorities that it would be better to release the ECM to the British 

than to make a third machine or an adaptor for the ECM to enable 

intercommunication with the TYPEX. In an undated memorandum 

(April 1942?), the chief of the Navy cryptographic unit recommended 

the release, pointing out the advantages and disadvantages (Incl. 4). 

His recommendation was disregarded. In a memorandum dated 16 September 1942 (Incl. 5), .the Chief of OP-20 (Navy cryptologic organization) 

pointed out quite clearly to the Director of Naval Communications 

that "If our plan of war is to keep England from falling and to 

prosecute the war with all our national resources to a successful 

conclusion, our present policy /.Of withholding the ECMJ is unsound 

and should be reversed without delay." However, his recommendation 

was also disregarded and work continued on the development of the 

CCM. One of the forms which the CCM took was the CSP 1700. This is 

a machine built upon the ECM chassis but with only five rotors. (It 

is similar to Army's SIGROD.) The British were provided with quite 

a number of CSP 1700 machines during the war. Whoever knows the 

cryptographic principles of the ECM-SIGABA and has a CSP 1700 can 

build an ECM easily enoug~. 

2. The CCM proved to be fairly satisfactory as a solution to 

the problem of Combined communications but British pressure to get 

the ECM-SIGABA. continued. In 1944 there was another drive on, baa.a.use of some doubts as to the security of the CCM. But the U.S. 

attitude became even more firm and strenuous endeavors were made to 

prevent the British from seeing the machine. Joint regulations had 

been adopted (Incl. 6) and it was agreed that at no time would the 

SIGABA. be put aboard a British vessel or in a British headquarters 
\ 

CSGAS-14 

SUBJECT: 

aREF ID:A2435719 A 

·1~? ~ffiRH· 22 Sep 49 

Background of Policy in Regard to Making SIGABA Available to 

the British 

except under custody of a U.S. Liaison team. These regulations were 

carefully observed but in at least one instance a failure occurred 

(Incl. 7), and ~here was good opportunity for the British to study 

the equipment in detail, for not only was the machine available but 

also complete instructions, etc. There may have been several other 

opportunities for learning details about the machine, but it is 

difficult to document them. A copy of a document (SIGKKK) giving 

complete details and drawings pertaining to the SIGABA was lost in 

Burma and never recovered. (See Incl. 7a~ This much we do know and 

can document: In the Combined conferences held in the spring of 1947 

with a view to replacing or improving the COM, the British frankly 

admitted that they not only understood the basic cryptographic 

principles of the ECM but also had incorporated them in a new 

machine for radioteletype communications. They explained their 

understanding of the cryptoprinciples and their explanation was 

correct. 

3. a. Early in 1947 the British officially raised the question 

of a replacement for the COM, stating that the present CCM was not 

secure enough for the Combined communications of another emergency. 

They sent Capt. Wilson to Washington to discuss the matter (Incl. 8). 

Prior to holding Combined conferences, there was a Joint meeting to 

arrive at a U. S. position in the matter. 

b. The Joint meeting was held on 23 Jan 47 and it was 

decided that the first meeting with the British would be confined 

solely to a discussion of,the COM and that there would be no discussion 

whatsoever as to the possible use of the JOC:M (Incl. 9). On 28 January 

47 the first Combined conference was held. It was at this meeting that 

Capt. Wilson disclosed that they knew the cryptographic principles 

underlying the ECM and would like to embody them in a new CTM but if 

the U. s. insisted on withholding the :EX)M they would like to present 

a wholly new idea. The British did not want to disclose their idea at 

that meeting, which then adjourned to allow U. s. representatives to 

confer among themselves and.perhaps to get some indic'a.tion from higher 

authority as to whether a policy decision would be made regarding the 

long-term retention or scrapping of the ECM principles (Incl. 10}. In 

the subsequent Joint discussions the Army maintained the view that in 

view of all the presently-known facts it would be to the advantage of 

all concerned to let the British have the SIG.A.BA. But despite all the 

arguments the Army representatives could present to the then Director 

of Naval Communications, he remained adamant against disclosure. It 

• 
CSGAS-14 

SUBJECT: 

fiEF ID:A2435719 e 

m~ SEC~H 22 Sep 49 

Background of Policy in Regard to Making SIGABA Available to 

the British 

happened that during one of these Joint discussions in the Director's 

office in the Navy Department, Capt. Wilson was in the building and 

was asked if he would be willing to disclose the radicall,y new British 

idea for a new cipher machine without any strings attached to his 

disclosure. He stated his willingness to do so (Incl. 11). It was 

thereupon agreed by the A:rmy and Navy representatives in Joint session 

not to go to higher authority with the question of a possible change 

in policy but to see first what the British had to offer. On 21 February 

in a Combined meeting (Incl. 12) the .British disclosed the principles of 

their proposed new cipher machine, which they called the RM 26. On 

25 February at a Joint meeting the RM 26 was discussed and found to be 

wanting in practicability. ·on 28 February at a Combined meeting the 

U. s. position was stated in writing (Incl. 1.3) and it was made clear 

that the U. S. found it impossible to embark upon the development of a 

new CCM based upon the principles of the RM 26. 

c. In view of the impossibility of getting the Navy to recede 

from its position on the matter of disclosing the EXJM the Army had 

agreed to continue to withhold the EDM-SIGABA from the British and to 

collaborate with the Navy and the British in attempts to improve the 

present CCM. A Combined report of the discussions was drawn up and 

agreed upon at a Combined conf'erence on 4 March 1947 (Incl. 14). One 

of the important points of the agreement was that Combined security 

regulations would be established. (This has been done.) An:- Army 

report of the Combined and Joint meetings was made to the Chief of 

Staff (Incl. 15) and likewise a Navy report was filed by Admiral Stone 

to the Chief of Naval Operations (Incl. 16). 

d. EXperimental work, conducted almost entirely by Navy, to 

improve the CCM was continued throughout 1947 and for a time .Army was 

hopeful ,1£ good results because of Navy optimism concerning the outcome. 

There also were some Joint meetings and discussions during that year 

(Incl. 17). But progress was very slow and the British were getting 

impatient. .Almost a year had gone by and still there was no improved 

CCM nor any signs that one was about ready to be submitt~~ ~o,them for 

study. On 16 February 1948 there was another Joint meeting"'to'discuss 

a new British paper (Incl. 1f) on the subject. It summarizecl and 

presented a rather dark but accurate picture of the situation as to 

the possibility of improving the CCIII and concluded that "every effort 

should be made to reach agreement with U. S. authorit,ies in the 

design and production of a brand new cipher machine for Combined 
-. I ' • 

CSGAS-14 

SUBJECT: 

22 Sep 49 

Background of Policy in Regard to Making SIG.A.BA Available to 

the British 

purposes." 'rhere were Joint meetings and discussions throughout 1948 

(Incl. 20) but little further progress was made. About the only 

outcome of Navy's experj.mental work was the production of a modified 

COM which they called the BCM. The modification principally consisted 

in making two of the five rotors step backward; there was also a change 

in the order in which the rotors stepped. These brought some improvement in security but in Army's opinion the additional security was not 

too important. The krmy representatives felt that it certainly would 

not satisfy the British, to whom the proposed modifications had not 

yet been communicated, and who were still waiting for an answer to the 

question raised early in 1947. Also, the idea of backward stepping of 

two rotors was a feature of the Navy's CSP 2900,·a modification of the ECMSIGABA and the krrrry' pointed out that one of the Navy's own motives for 

producing the CSP 2900 was to have something that the British would not 

know about in connection with the ECM-SIGABA. There.fore, to disclose 

the BCM would militate against the idea that the CSP 2900 would be 

wholely unknown to the British. 

e. In the meantime the British had been doing some work in 

the development of their RM 26 machine. But by the end of 1948 or 

early in 1949 it had become apparent to them that the U. :S. experts 

had been correct in their contention that the RM 26 was impractical 

from an engineering point of view and further work on this machine was 

abandoned. Two full years had gone by and they had neither a new 

machine of the~r own nor an improved CCM for Combined communications. 

f. Tnerefore, the British decided to reopen once more the 

question of releasing the ECM-SIGABA. In May 1949 they filed a paper 

{RIXJ 5/87) and in July they filed a modified paper (RDC 5/99) on the 

subject. 

g. The British JCS paper was referred to the Joint Security 

and Cryptographic Panel of the Joint Communications and Electronics 

Committee for study and recommendation. The opinion and action of the 

Panel is summarized in Incl. 21. It is important to note that the Panel 

was unanimous in wishing to recommend acceptance of the 2d British 

proposal--release of the :&:M. 

4. To summariz~ my own opiniom 

a. The Navy has consistently taken and has more or less 

stubbornly adhered to a position against disclosure, even when it 

became clear that the British knew the basic principles. The Navy felt 
-

CSGAS-14 

SUBJECT: 

. tJEF ID:A2435719 e 

l~? ~[C~H 22 Sep 49 

Background of Policy in Regard to Making SIGABA Available to 

the British 

and apparently still feels that there is security value in withholding 

the engineering know-how. But even that has become a weak argument 

since the British have had OSF 1700 machines. If the British wanted · to "break faith" with U. S., they ·could build ECM 1 s without our knowledge 

or permission. It is my assumption that they do not wish to do this 

on such a basis; also, it ~$ possible that they do not wish to build 

the machines themselves--it is possible that they may want to buy 

them from Teletype Corporation in order to avoid a great and unnecessary 

research and development expense. That would.be logical from the 

British viewpoint. Moreover, they know that even if they should 

secretly build ~M's for themselves, this would not solve the problem 

of Combined communications. Sooner or later they would be forced to 

tell the U. S. that they have their own ECM' s--and the 11cat would be 

out of the bag. 11 It seems to me that they have looked ahead and have 

seen what embarrassment there would be in such a course and have wisely 

decided to try once more to get the I!l::M without subterf~ and to legitimatize 

their possession of knowledge of its principles so that'l:hey can make use 

of that knowledge legitimately. 

b. The krmy had originally and up to the early part of 1947 

shared the Navy viewpoint. But after the Combined conferences in the 

spring 0£ 1947, the Axmy changed its view and was willing to release 

the SIGABA to the British. It only concurred with the Navy in the hope 

that Navy contentions that the COM could be satisfactorily improved 

would be sustained. Since those contentions have not been sustained, th~ only logical course is to accept the 2d British proposal, viz., 

officiaJJ.y to release to them the cryptographic principles of the F.CMSIGABA and let them have full details of its construction. They will 

then be in a position to use this knowledge legitimately and without 

embarrassment, and steps can then be taken very speedily to arrange for 

Combined communications in a way that will be mutually eiatisfactory. 

21 Incls 

7 

C/JJ iMu1i~~ J.-~~g_J.l~·~·-'~' WILLIAM F. FRIEDMAN 

Special Assistant