Special COMSEC Support Detachment-Tan Son Nhut
By Andy Csordas, Spec 5
I entered the Army after a deferred enlistment during the Tet offensive of 68. I had become 1A and knew it was just a matter of time until I was drafted, so I enlisted to pick an MOS. After many weeks of training I finished with an MOS of 31S30, Field General Cryto Repairman, depot level. I spent some time in Detroit and about a year in Cleveland before receiving orders for Vietnam. Through some unusual circumstances I was led to believe that I was going to Vietnam on a special assignment and fully expected to live in a hotel and wear civilian clothes. I will never forget the belly laugh by the E7 when I approached him after I arrived in country and asked about my “special assignment”. Needless to say mine was no more special than anyone else’s assignment.I processed into my battalion level outfit at Long Bien June 1, 1970 with only nine months left on my enlistment and ended up at Tan Son Nhut where a friend from school had one month left in country. At the time we lived in the upstairs of a barracks at MACV Annex. The AFVN guys all lived downstairs. About a month later we moved into our repair compound in the H3 Heliport across from the Post Exchange. We repaired classified gear and our repair compound had to be manned 24/7. Our troop strength was steadily being reduced and we did not have enough manpower to man 24/7 unless we lived in the repair compound, which was one medium sized building, a bunker and two sand bagged conexes with a locked fence around the perimeter. We were surrounded by the heliport, a lot with helicopter part containers, Camp Alpha and the road to the H3 Terminal.
We mostly repaired cryto gear for other countries troops including ARVN, Australia, and Korea, but by far the largest work load was from the ARVN’s. Some equipment just showed up, we were not sure where it came from so it may have been from US outfits. Our battalion level unit was located in Long Bien and there were detachments like ours, Special Comsec Support Detachment, from the “Delta to the DMZ” as they used to say. Ours was one of the larger units with approximately 18 people assigned when I arrived in country which was reduced over time to approximately 9-10 when I came home at Christmas 1970. That included one guy who lived at the ARVN KL-7 operator training base at Vung Tau. He brought his tanned body, along with broken KL-7’s, back to our compound once a month on pay day. Some of the other detachments were only one guy working in a trailer at a base camp.
Most of the gear we repaired was older equipment including more KL-7’s than we ever wanted to repair from the ARVN’s. The ARVN’s were not given access to modern Cryto gear. We did work on newer equipment like KW-7’s, KY-28’s, KY-38’s and older but still much newer than anything the ARVN’s used the KY-8.
Jerry Proc has a good Cryto site at, http://www.jproc.ca/crypto/menu.html, which includes lots of great information and pictures of the gear we repaired and many other items and articles.
The KW-7’s were used for teletype transmission, typed on a keyboard at the point of origin, which provided a paper print out and a punched paper tape at the receiving end. I am told the KW-7 was used for radio traffic as well in other situations but our application was strictly teletype through landlines. These units generally came from the Aussies and other allies.
The KY-8, KY-28 and KY-38 were all used to encipher radio traffic and were all compatible if set to the same settings. A KY-8 was transistor technology and quite large, approximately the size of a counter model microwave oven of today, and was typically Jeep or truck mounted.
The KY-28 was typically installed in a helicopter; you may have seen it as a grey box mounted under the pedals on the left seat of a Huey approximately 6” x 8” x 12”. The KY-38 was carried on the back of the grunt radio man. The unit with the battery attached was approximately the size of three cartons of cigarettes.
All of these units used analog technology, whereas the KW-7 used digital technology. If listening on the same frequency being used with these units all you would hear is static and noise unless you were using a compatible unit with the same setup. These units were able to save lives on a daily basis by keeping our plans and movements out of the other side’s hands.
The KY-28 and KY-38 had quite sophisticated technology for the time. They used six or eight layer circuit boards and IC chips which were not at all common at that period of time. The units had individual electronic components including transistors, capacitors, resistors, etc. But the there were a number of chips that provided much of the enabling circuitry. These chips were very basic and quite large by today’s standards, 8 or 12 legs, 3/8” square and perhaps 2” long, but were very sophisticated for the time. It took lots of deliberate care to properly solder a chip through all circuit board layers and not end up with a cold solder joint. After soldering a chip in place we would mix epoxy and attach the new chip to the circuit board to minimize movement, particularly on the KY-38 which received a lot of shock and movement on the back of the grunt in his normal course of the day.
The KL-7, used by the ARVN’s, was technology left over from the Korean War and was introduced in 1953. It was a stand alone portable unit enclosed in a fiber glass case. It printed an encrypted message on a paper tape in five letter groups. After every five letters the unit placed a space on the paper tape. Encryption was provided by a series of eight rotors that were set to a specific code by the operator. When the encrypted message was typed into the KL-7 with rotors set to the same code a clear message was printed. This unit also used four vacuum tubes, with two extra tubes plugged in the board for spares. As I said it was old technology and was quite similar to the enigma machines used by the Germans in WWII. There is a great book, A Man Called Intrepid, which includes WWII cryto intrigue and information about the Enigma Machine by William Stevenson.
The KL-7 base board had a series of posts on the bottom side which had a wiring harness soldered to the posts, not printed circuits. These units were thrown in the back of trucks, dropped all the time and generally had a pretty rough life which resulted in damaged vacuum tubes and lots of cold solder joints on the main board. They also came into the shop covered in Agent Orange. Frequently we could not find a failed component so we just re-soldered all of the connections on the wiring harness posts which would fix the problem. The continuously rotating print wheel had critical timing which sometimes required a speed adjustment on the motor to print the correct letters.
Another constant problem with the unit was corrosion on the rotor contacts. After every character was typed into the unit the rotors would step one notch. If there was corrosion, however minor, on the contacts which prevented a complete circuit through the rotors and unit the rotors would stop stepping. The normal operator kit included contact cleaners, can you say an erasure, for this problem. When the rotors stopped stepping on the units we were repairing in the shop we would sometimes strike the rotor basket with the handle of a large screwdriver and it would start working again. It had to be difficult for the operators working under duress.
The KL-7 had a bridge rectifier that used twelve diodes to convert AC power into DC power. Most bridge rectifiers use four diodes, but these older diodes required three on each leg and were notorious for their failure rate. At one time we had over 100 KL-7s’s on the shelf waiting for diodes, the diodes were always on back order. One day we received all of the diodes we had on backorder and more. The newer diodes only required four for the entire bridge rectifier and were part of a retrofit any time we had a unit in the shop. Bad diodes or not, every unit got the new diodes from that time forward.
We then got to work some pretty long hours, 12-16 hour shifts seven days a week until the back log of repairs got back to almost nothing. We worked almost exclusively on the KL-7s during that time period and even got help from other techs who arrived from the other detachments to help.
I may add some other details in another post, but suffice to say I received an early out to come home and start school in January 1971. I was fortunate enough to be home to have Christmas with my bride of one year who still puts up with me!
June 19/10