SSM-33 (SIGTOT) Cryptosystem

The SSM-33 was a newer version of the 131B2 table.  It consisted of a gray interface/mixer  box about the size of a desktop tower computer, a special Model 14 tape reader (TD), and  a Model 14 KTR (Keyboard Typing Reperforator) .  SSM-33 was issued to the Koreans fighting in the Vietnam war.

This system used a special "one time tape reader" which was also used with several crypto mixing machines.( e SSM-33, 131B-2). The distributor head is different than a regular Model 14 Transmitter Distribution. It has a clutch  control magnet that was "stepped" by the crypto device in conjunction with a classified traffic message. This system was called "SIGTOT".

The distributor commutator of the special TD is made up of two concentric conducting rings mounted on an insulated disk. The outer ring is divided into five large and 10 small segments as compared to seven on the corresponding ring of a regulator TD. It's important to notice these two differences in TD distributor segments, as it indicates that the mixing (Crypto) unit was clocked to produce a cipher tape.

The SSM-33 external Teletype gear could be configured in a number of different ways.  In Communications Centres, this was usually  done via a teletype patch panel. One specific configuration might have a KTR14, a normal TD, a special TD hooked up to the SSM-33 along with a Teletype page printer for set up and to read what the distant station was sending you.

A punched, plain language  (P/L) tape would be produced on the KTR14. Next, the P/L tape  would be mounted on the normal 14TD while the special 14TD would have the keytape mounted and ready to go.  When the operator initiated transmission, the P/L tape was “mixed (Boolean Exclusive OR function) with the keytape and the ciphered message was sent across the  link to the far end.

Components of the SSM-33 tape system were never classified. This equipment is referenced in document TM 11-2222.  When the  manual talks about a "Receiving" TD, that's means the device local to the operator and *not* the far end.

Some parts of an SSM-33  cryptosystem with a spare synchronous TD motor. At the top is the 14 KTR teleprinter (Keyboard Typing Reperforator). This unit normally would be used to prepare a clear text copy of traffic to be transmitted into the SSM-33 for encryption and transmission. The clear text would be printed on the tape as the holes were being punched, so the operator could check the data stream.

Almost all traffic was punched up on tape so an operator could check it and also circuit time was at a premium. Once the operator established the circuit, clear text tapes would be fed into the SSM-33 and encrypted.

Rather the special TD, a normal  TD is depicted in the photo. A  normal TD  has two cables and it also has a tight-tape stop lever coming out of it’s left side which a special TD does not have.

SSM-33 cipher interface and mixer unit  front view with line relay doors closed. 
Front view with doors open to show the polar line relays. 
Rear view with cover on.
Rear view with cover off.
All photos in this table by Don Robert House.

Commutator rings on a normal  14TD. This example is lacking connecting cables. Its slip ring connections plug into mating contacts on a table teletype, (E-bay photo)
SIGTOT - A slightly different version of the special 14TD .(Photo by Ralph Simpson)
View of commutator on special 14TD. Also note that the device lacks the  tight-tape stop lever. (E-bay photo) 
Commutator segmentation on special 14TD. (Provided by George Mace)

ssm33_clear_text_distributor_s.jpg This is the wiring diagram of the normal 14TD ( model TT-52). Click on image to enlarge. (From TZL2524A. Provided by George Mace)
ssm33_tt25_wiring_diagram_s.jpg This is the wiring diagram of the special TD, model TT-25. Click on image to enlarge. (From TM 11-2222. Provided by George Mace)
George Mace offers some humour regarding the SSM-33. "It used six 255A polar relays to mix plain text and one time keytape. In 1958, on Eniwetok Atoll, during thirty five nuclear tests, the main Communications Center for Operation Hardtack used an SSM-33. Within the crypto maintenance shop, where I worked, we had a test device used for adjusting these 255A relays. A correctly adjusted relay would produce crisp, sharp teletype signals, especially on the leading edges (rise time). During nine months on the island, I spent untold hours adjusting these relays to satisfy my Warrant Officer maintenance chief.  When you're in your early twenties and water skiing in the lagoon is just outside the green door, a mediocre relay adjustment seems adequate.  NOT SO- Mister Learner taught me!! It got so that I could adjust a relay where it seemed that just blowing on the armature would change it's position".

Contributors and Credits:

1)  Don Robert House <k9tty(at)>
2) George Mace <gmace8(at)>
3) Ralph Simpson <ralphenator(at)>

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Nov 4/12