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WAR DEPARTMENT 

OFFICE OF THE CHIEF SIGNAL OFFICER 

WASHINGTON 

March 24, 19.36 

8 

Research & Development Division (THRUa V!.P.& T. Div.) 

1. Attached hereto is a ?roposed modification in Converter 

Type I.1-134-Tl. Although all work on this model has been suspendeo., 

pending the development of T2, it is thought t..lis.t the modification 

herewith proposed has sufficient merit to warrant consideration in 

connection with further cipher machine devolopment,and for this 

reason the modification should be covered b,y patent to protect the 

government's interest. 

2. At an early date I hope to draw up the specifications for 

pstent application. 

Attached: 

1 Dra~iir.g, 

Description. 

1st Memo Ind. 8 

OCSigO, War Plans & Training Division, 1darch 24, 1936 - To: Research 

and Development Division. 

Forwarded. 

Attached: 

(no change) 

IT. S. Ru"D.bough, 

:uJajor, Signal Corps. 

Declassified and approved for release by NSA on 07-21-2014 pursuant to E.O. 

13526 

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March 12, 19.'36 

Modification 1n Converter Type M-134-Tl 

(U. s. Patent 2,028,772 of Janwu:y- 28, 1936) 

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1. In u. S. Patent 2,028,772 the ciphering commutator is started 

and stopped, as controlled by the opening and closing of the comparing 

circuit {composed of the set or ten contact levers and associated twenty 

contact points). Since the latter is controlled bf the cipher-key tape, 

the action of the commutator is very irregular. Since the inertia of 

the commutator is considerable, it is difficult to speed up the operation of the system and still be able to stop the commutator rapidly and 

accurately in its displacements. 

2. When the indicating devices are glow lamps it is of course 

essential either to stop the commutator long enough for the eye to perceive the character illuminated on the indicating bank or to provide a 

system of self-locking relays in series with each glow lamp so that if 

a glow lamp receives a momentary impulse through it, the self-locking 

relay acts to keep the lamp illuminated long enough to permit of noting 

the character illuminated. In either case this would complicate the 

mechanism. 

3. I have conceived of a method of operation which not only overcomes the foregoing objections and disadvantages, but also simplifies 

the system considerably and at the same time simplifies automatic recording of the resultants. 

4. The basic principle of the modification is as follows: Instead 

of employing the comparing circuit to control the starting and stopping 

of the commutator wheel,, let the wheel be kept in constant, regular rotation, and let the comparing circuit merely determine when electric potential is applied at the keyboard. Thus, when a key of the keyboard is 

depressed no current reaches the indicating bank through the cipher commutator until the comparing circuit is completed. Since the latter 

event is controlled by the cipher-key transmitter, it is obvious that a 

result will be indicated on the indicating bank once per revolution of 

the commutator,, but the exact instant when it will be indicated is a 

function of the character on the cipher-key tape. If the time required 

for one complete revolution of the cipher commute.tor is regarded as 

being divided up into 26 equal intervals,, the cipher-key tape merely determines at which of the 26 intervals the comparison circuit will be 

completed and there.fore which of the 26 possible equivalents will be 

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indicated for the key being depressed during that revolution of the 

commutator. Since this action can take place instantaneously, the 

commutator can be rotated quite rapidly, and though the ciphering 

action is irregular in that successive encipherments take place at 

irregular instants of the cycle of rotation within successive revolutions ot the commutator, the action is so rapid:cy- performed that the 

operator does not notice the irregularity, and a cadence in keyboard 

operation is perfectly possible. 

5. The modified circuit arrangements are shown in accompa:o;ying 

Fig. 1. 

6. Obviously, for this type of control, glow lamp indications 

are not suitable because the action is too rapid; or if it is slowed 

down, one loses most of the advantages of this modification. The 

system is much more suited t.o automatic recording, by controlling the 

keyboard of an associated typewriter, or the printing action of a rotating type wheel. 

7. If a rotating type wheel is used, the comparison circuit, in 

addition to including in series with 1 t the tape-stepping magnet, would 

also include the relay controlling the time of delivery of the printing 

impulse. The type wheel would have to be rotated synchronously" with 

the cipher wheel. 

9;.J~~~ William F. FriedJilan. 

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