The KL-7 on Merchant Ships during the Falklands War

TSEC/KL-7 Photo © D. Rijmenants

The TSEC/KL-7 was the first tactical lightweight rotor crypto machine with electronics, developed in 1949 by the ASA and AFSA. In 1953, the NSA introduced this cryptologic marvel as standard crypto device for the U.S. military. Soon after, NSA proposed to share the KL-7 with their NATO allies to improve communications security.

The machine had excellent cryptographic properties and was certified for top secret messages. NSA did recognized that its cryptographic principles eventually would also find their way to non-military use in NATO countries, or might even end up in Soviet hands. Still, having such strong encryption, the machine was never meant to end up in non-government civilian hands. Nevertheless, there are a few rare cases when civilians did work with the KL-7.

One such case were civilian radio officers on merchant ships during the 1982 Falklands War. The Falkland Islands (Malvinas in Spanish) is British overseas territory, disputed since long by Argentina. On April 2, Argentina invaded the Falklands and the British government sent a huge naval task force with two aircraft carriers, 65 Royal Navy and Fleet Auxiliary vessels, 62 merchant ships and two ocean liners that carried two brigades.

To sail that task force 6500 nautical miles or 12.000 Km across the Atlantic was an enormous logistic operation and they needed vast quantities of fuel for the trip and to keep the task force operational near the Falklands. The British Ministry of Defense chartered a large number of commercial merchant ships to support the operation, a procedure called STUFT (Ships Taken Up From Trade).

One of these STUFT ships was the Eburna tanker that carried fuel oil, diesel and aviation fuel which had to be transferred by RAS (replenishment at sea) to other ships. This involved two ships steaming alongside each other at close range while maintaining a steady speed throughout complex anti-submarine manoeuvres. The communications between the task force and the STUFT ships had to be secure and the Eburna radio room received a KL-7.

The Eburna fuel tanker (source: helderline.com)

Bernard Kates was the radio officer on the Eburna. He had no experience at all with naval communications nor crypto systems and had learn the basics of cryptography and operating the KL-7 within very short time. Fortunately, he had a radio officer from the Royal Fleet Auxiliary who knew the KL-7 very well, as assistant.

 

They received encrypted traffic by teleprinter broadcast (FEC mode) via Portishead Radio and transmitted Eburna's encrypted replies using ARQ (Automatic Repeat Request protocol). They managed to keep the radio room going, processed encrypted traffic and maintained a 24 hour watch on the UHF tactical net.

Their KL-7 had an extension to read punched tape and they attempted to receive traffic by setting the teleprinter to copy to both tape and paper, but as traffic was too heavy and mixed with messages from many other ships they had trouble separating the punched tapes correctly. They therefore let the teleprinter simply print the messages and then typed the ciphertext onto the KL-7. The deciphered text, printed on gummed tape, was stuck onto a message form and delivered to the Captain, although they sometimes had to translated the "navy-speak" into plain English to make it understandable to their civilian Captain.

The system indicator "FDDND" was always the first group of ciphertext. They would set up the KL-7 following the key setting instructions for that day, then switch it to "P" and type in that group, then switch to "E" and do the encryption. The daily machine settings were printed in a booklet which had the edges of all its pages stuck together, one page per day and one month per booklet. To set up the machine you would peel off the sheet from the previous day, revealing today's settings. Used sheets would were torn out and incinerated.

Eburna's KL-7 was supplied with only one rotor cage and one set of rotors. According to the instructions, the rotor setting were changed at 00:00 UTC and the key sheet of the previous day had to be destroyed. Thus, when a message of the previous day arrived a few hours later, they could not go back to the old settings. They decided to keep the old key sheet for an additional 24 hours to go back if they had to. In the military, the KL-7 was usually supplied with two rotor cages, and the rotor cage with settings of the previous day was kept the next day. Going back then simply meant swiftly detaching the current cage and attaching the old one. The Eburna radio office did not have this luxury.

The KL-7, rotor set and setting instructions were supposed to be kept in the safe but the Eburna didn't have a safe, so they kept them in a cupboard. They assumed there were very few spies running around in the middle of the South Atlantic and their solution was probably secure enough. Bernard also recalled rewiring at least one of the rotors every month, and that it was quite a fiddly task involving many small parts.

Bernard also commented on the KL-7 simulator. "I downloaded the KL7 simulator and am having fun with it reliving old memories. The only thing the simulator doesn't do that the real machine did is to fail occasionally (actually quite often!) due to dirt under the keyboard. In accordance with Murphy's Law it would always do that when urgent traffic was on hand. Then there was nothing for it but to take the machine apart and clean it out". The need for intensive maintenance was indeed one of the KL-7's disadvantages and essential to avoid the so-called dead-rove.

The Navy didn't quite understood how merchant ships operated or how they were equipped, and never realized that keeping a 24 hour radio watch with only two men for the duration of the entire campaign was a daunting task. The Navy also expected them to know how to handle a tactical radio net and encrypt figures and phrases using NATO code books.

At first, Bernard had no idea what was going on and it took several days to work it out. He noted that a tactical radio net in a war zone is not the best place to learn military radio procedure. To their excuse, the Navy also had a daunting and unprecedented task to compile a huge naval task force within days.

The Eburna story is a rare example of civilian merchant radio officers that worked with the KL-7. Undoubtedly, more people outside the military, intelligence and state departments worked with this beautiful cipher machine. Let's hope their stories and will also be recorded some day, before that fascinating history is lost.

In the end, the Argentine forces surrendered after 74 days and many lives were lost on both sides. The 1982 Falklands War was probably the last time the KL-7 was used during combat operations. 

The KL-7 on Merchant Ships during the Falklands War (pdf) is the story from radio officer Bernard Kates.

More on this iconic Cold War crypto machine, including all technical details, its development, operational history and many related NSA and NATO documents at the TSEC/KL-7 ADONIS & POLLUX page

More about the Eburna tanker at Helderline.com and a detailed history of the Falklands War is available at Naval History.