, 

.. • REF ID:A522107 • 

WAR DEPARTMENT 

SIGNAL CORPS LABORATORIES IN REPLY REFER TO 

EXPRESS ANO FREIGHT ADDRESS 

LITTLE SILVER, NEW .JERSEY 

Ml'. William F. Frfedman, 

Cipher Section, 

FORT MONMOUTH 

Office ot the Chief Signal Of'f icer, 

War Depar1ment, 

Washington, D. c. 

My dear Friedman.: 

GA.G:D 

POST OFFICE ADDRESS 

OCEANPORT, NEW .JERSEY 

March 11, 193~. 

With ref'erence to your letter of February 24, 1933 the circuit 

as proposed by you for adding an additional.tape transmitter to the 

cipher me.chine has been checked and will undoubtedly work correctly ·as 

intended. The photosta t copy of your sketch is being retained for f'uture 

reference. 

With regard to sending you an additional tape tranEIDi tter, you 

are adv! sed that there are at present only two such tape transmitters as 

modified for application to the cipher machine. You have one of these 

transmitters and the other one is installed on the cipher machine held 

at these Laboratories. It is not desired to release the one with the 

laborator.r model cipher machine but it is considered preferable to modify 

an additional standard 110 volt tape transmitter. In order that you Day 

clearly' visualize thv work required in this modification the tape stepforward magnets of the standard tape transmitter were rewound for operation 

on 8 volts. In addition to this you will recall 1hat the standard tape 

transmitter presents all contacts in common tor both spacing and marking. 

It was therefore necessary to provide individual insulated front and rear 

contacts in these transmitters and to wire those contacts to wedge terminals 

as in your model. It is estimated that the work required in this ·connection 

from a Qbop standpoint would require approx:lmately one weeks time. The shop 

at the present time is vecy- busily engaged in certain radio work o:f' a high· 

priority as directed by the Chief Signal Officer. In order to disrupt such 

priority it would be necessary that Y'OU take the matter up with the .. 

Engineering & Research D~Vision of your office. 

In any event, you should present the desire for an additional 

tranamitter to the Engineering & Research Division in order that these Laboratories may be officially athorized to proceed w11h the work of the modification of the additional tape transmitter for the cipher machlne. such an 

JA'pproved for Release by NSA on 11-19-2013 pursW:Qr! to E.O. 1352§ 
• REF ID:A522107 • 

Le. to :Mr. William F. Friedman 

authorization will 'then permit the modification ot the transmitter wlieiL circumstances permit. 

Referring again to the circuit modUication, while ilS·:· ·stated before 

there is no doubt about the circuit working electrically, but f'rcm the standpoint 

ot cryptographic possibilities it seems to me that you are in degree reducing 

the secrecy. In the f'iDal. analysis the secrecy of' our machine depends upon the 

commutations of' the cipher wheel. .A.side tran all other elements, that is, the 

position of the wheel actually determi~e the cipher letter. It would seem then 

that in reducing tb.e resultant average number of' positions or steps would in 

turn increase the frequency of appearance of' au;y given cipher character. However 

this is a matter for you to determine. 

. It would a,Ell'.ll tran the standpoint or distribution of' ta.pea or machine 

setting to a given receiving station or net that the netter coald be very 

satisfactorily arra:aged if' we would provide tbe additional five manually opera-

. ted drums by means of' which an arbitrary sequence could be set up i'or each and 

every message transmitted, holding the tape proper constant. The sequence of 

this drum arraJgement could be noted on the bottom of each message transni tted, 

as for example a,y,t,x,g, etc. 

In sunnnation of the above it is recommended that you contact representatives of 1he Engineering & Research Division and request that a directive be 

given these Laboratories for the modification of an additional tape transmitter 

for your experimental use in conjunction with the Converter, type iM-131-Tl. 

Very truly yours, 

GA.G:D 
f ... "'. 

/ ·i -~ .. 

> 

• REF ID:A522107 ..• 

Date..._.._ __ ._.._._. __ ..,._ 

Rec.elvecl from the st.pal Corps I.aboratorlea letter data4 :rebruary 27 1 

1933, e11bject,•Deacript1on and Operating lnatructlon:e tor Convert.er, t;vpe 

M-134-Tl 1 , tile ProJecti 86. 

(same) - (lanJc)