REF ·ID-:A2435737 

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Declassified and approved for release by NSA on 09-19-2013 pursuantto E .0. 1352a 
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IN REPLY 

REFER TO 

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OCSig0.461 Codes 

(4-l_0-42) 

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WAR DEPARTMENT SPSIS-3 

OFFICE OF THE CHIEF SIGNAL OFFiCER. 

WASHINGTON , April 10, 1942 

Si!cret 

lr:El.:ORAlJwll TO: Assistant Chief of Staff, G-2 By :\uth.11;-ily of th~ 

£1.irf_ Si;'.">31 0 ·f:r,-; 

67~--.. ~~-~;~~~ : ~ 

1. C-olonel Til t."!'.an, Officer in Charge of the 11 S~rvices 

Division" of the British C!"JPtographic and Cryptanalytic Service has 

presented details of and has requested our comments and criticisms on 

the cryptographic systEms which they are now using and propose for 

future use in their field forces. Exar.~nation of these systems convinces us that they are very slow; complicated, and impracticable for 

our use in case our field forces had to work and cor.u:nunicate vr.i.th 

British forces in joint operations. It is furthermore believed that 

the degree of security afforded by the British field systems is inferior to that afforded by either our present strip ciphers based 

upon Cipher Device h:-138-A, or the proposed r.:-209 Device. 

2. I~ is thought very' desirable that we confer with Colonel 

Ti,ltman with respect to the possibility of their adopting our strip 

cipher systems as -well as the 1~-209 Levice, at ieast for joint use. 

It would be conducive to the security of our own forces when operating 

with the British to have them use the strip cipher system and the 

M-209 Device but vii. th t}1eir own keys. -

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3. . The 1:-138-A Device is already kno-Tm1 ·ta' and is used by 

the Canadian Air Force in certain types of communicatron 11-i th our mm 

Air Force. The M-209 Device is also known to the--Canadian and the 

British Governments, since. it is a device that wa«s procurable coinmer'-

cially in lirni ted quantities before its adoption b:\r us for field use. 

-= ·-!' ~1- -:i ,r.: 4. It is proposed, if possible, to work out with Colonel 

Tiltman the basis for joint cryptographic systems using the Y.-138-A 

and 1,:-209 Devices so as to permit of expeditious intercommunication -

between American and British uni ts working together. However, these 

systems would be in addition to cryptographic systems ( usin~; these 

same devices) which would be restricted in distribution to American 

·_units, and which would therefore not be readable by the British. The 

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discussions would specifically be restricted to these systems and • 

devices and vrould exclude any discussion of our ·ele'ctrical converters. l 

UNITED 

STATES 

SAVINGS 

OONDS 

.INDSWIPS 

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.SECRET 

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OCSigO. 461 Codes 

(4-lO-!-i2) 

REF I~737 ~-·"f.,....~~JI•~· • 

SPSIS-3 

5. The U. S. Navy has been consulted in regard to this proposal and is agreeable thereto. 

6. Authority is requested to discuss in detail with Colonel 

I'iltrr.an the possibility of establishing joint cryptographic systers 

of the cateG0'1'..y mentioned in paragraph !~. 

For the Chief Signal Officer: 

Brigadier 

~s~ General, U.S. Anny 

MID 311.5 (4-10-42) 1st Ind. 

G-2, W.D. G.S., War Departrnent, 1fashington, D. c. APR 1 7194~ To: Chief Signal Officer, War Department, Washineton, D. c. 

Authority is granted to disc11ss the possibility of establishine joint cr.fPtographic systems using the M-138-A and 1~-209 Devices with 

Colonel filtman, O:fficer in Charge of the "Services Divisio.n11 of the 

British Cryptographic __ and Cryptanalytic Service. 

For the A. G. of S~, G-2: 

Chief, 

~~ Colonel, General Staff, 

Military Intelligence Serv;ice. 

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