Thursday, March 22, 2012


“During return flight of AF-1 from Dallas, we were working the aircraft via KW-7. The operator aboard the aircraft was so busy that he could not attend the ckt.”

SFC Carriger

The Orestes cryptosystem employed the KW-7. It was an on-line, send/receive crypto unit installed in shore stations and aboard ships. In one application, it was used for ship to shore and for intership radioteletype communications. To send messages over a secure UHF teletype circuit, a model 28 Teletype or reader (T-D) sent the prepared message to the KW-7 which in turn keyed a UHF transmitter in the AM mode. Note, that the KW-7 was not a totally synchronous unit, therefore, it required a phasing signal to be sent in order to attain a lock on the received signal. top. The circuitry was all solid-state and fit in a fairly rugged housing that featured a Tempest-sealed lid on top, removable for servicing. The KW-7 was also used aboard aircraft such as EC/RC-135's.


The original KW-7 had 30 fixed wires coming out of the bottom half of the key area. Using a daily key list, the operator plugged the wires into the top half a flat block. Many operators joked that part of the KW-7 course consisted of basket weaving since that seemed to be a prerequisite skill for this task. The task of coding the plugblocks was sometimes referred to as knitting. The wires were about 14 to 18 inches long and it took forever to get them all plugged in and still be able to close the door over top of them. There were metal loops provided to help shorten the slack but it was still difficult to get them packed in.

Many a time, a KW-7 used in flying command posts for TTY traffic would be pulled in for maintenance only to discover there were little black loops of wire hanging outside of the edge of the locked door because it was such a tight fit inside. This was frowned on since the purpose of the gasket was to reduce Tempest.

KWX-7 Front View. (Photo via E-bay)

This is the cockpit remote control unit which could operate the KW-7. It was made by Collins. The Orestes system, used in strategic and tactical environments, was not limited to ships and land based systems but also used in aircraft. The panel has 16 Clare Pendar switches: they are a combination of DPST, 4PST, latching, momentary and all are illuminated. Face plate is backlit as evidenced in the right photo. Switches have the following labels, TTY / KEY, KW-7, MODEM TEST, POWER, KW-7, 700B-2 1, KW-7 2, 700B-2 2, 700B-4, TE-204, KW-7 1, 700B-2 1, 700B-4, TE-204, KW-7 2 .
Dick Morris adds. "The Collins remote unit depicted above was actually part of the USAF ARA-60 system along with the TE-204A-2 synchronous modem. This system was on the airborne command post aircraft. The code name for the planes that I worked on at RAF Mildenhall in the U.K. was Silk Purse. Similar planes at Offut AFB were code named Looking Glass.

When new, these machines cost around $4,500 a piece and required 6 to 8 weeks of training in order to maintain them. KW-7's were also used in U.S. military radio shelters like the TRC-136, the GRC-122 and the GRC-142. The GRC-142 or GRC-122 used one or two KW-7s in a simplex or full-duplex HF radio link In either case they would have been attached to a GRC-106 radio set. Early shelter versions use Kleinschmidt teletypes and later versions use UGC-74 teleprinters. The KW-7 was self-synchronizing to the extent that whenever the other fellow stops sending, you push a button which sends out an initialization sequence to the other end to put it in sync.

KW-7 (Orestes)

KW-7's saw service in three variants. The original version used wire cords to set the daily key. Next, the plugblock version was introduced while the last variant used a paper card reader. Externally, one could tell the machines apart by the front covers. The original version of the machine had a flat, front cover. When the plugblock version was introduced the cover had a small square bulge. When card readers were introduced, the cover shape changed to a large rectangular bulge.

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