The KL-51 was an off-line keyboard encryption system that read and punched paper tape for use with teleprinters. It was developed as a follow on for the KL-7, but it used digital electronics for encryption instead of rotors. In NATO, the machine was called RACE (Rapid Automatic Cryptographic Equipment).
Frode Weierud provides some background information on KL-51/RACE.

"First of all, the machine is an entirely Norwegian development made by STK, Standard Telefon og Kabelfabrik, in Oslo. The development of the machine was started in 1973 as an off-line unit . STK, which perhaps is best known for the NATO and Washington/Moscow Hot-Line machine ETCCRM, (Electronic Teleprinter Cryptographic Regenerative Repeater Mixer), was already experienced in developing cipher machines for the Norwegian Armed Forces and Norwegian government customers. The previous developments were the three versions of the one-time-tape machine ETCRRM, another one-time-tape machine developed mainly for Norwegian government secure TELEX communications, the SELMA (Standard Electronic Letter Machine) OKA-150, and the transistorized version of the ETCRRM, the TCE 160 (Telecom Crypto Equipment 160).

In the mid 1960s ,STK moved away from one-time-tape and developed machines based on electronic key generators. The first was the TCE 180, also called Troll, and the Telex cipher machine Cryptel 240. TCE 180 was never commercialized since testing showed that major changes were necessary and the Cryptel 240 only had a very limited internal distribution in ITT due to the fact that the crypto algorithm was too good and too strong for use in a commercial machine. The authorities vetoed the sale of the machine outside a very limited number of customers and because the machine was not made to stringent military specifications it could not be sold to NATO or other military customers.

Therefore a new machine, the TCE 245, based on the TCE 240 was developed but with a much simpler and weaker crypto algorithm. This machine was more successful. In total , some 400 machines were produced and some were sold to oil companies and a few banks. The TCE 240 was introduced in 1967 and the TCE 245 a year later. All of these machines were designed by STK's chief engineer Per Abrahamsen, but who designed the crypto algorithms is not known,. However, it is strongly suspected the Norwegian professor Ernst S. Selmer was involved in the process of designing STK's crypto algorithms.

The machines had until then had been designed with transistors and integrated circuits, but in 1973, when the RACE design started, microprocessors started to appear and it was decided that this machine would use these new devices and that the crypto algorithm would be software based. It is possible this was the very first machine to use software based crypto algorithms and it proved to be an uphill struggle to have this new concept approved by NATO. The first deliveries where made in 1978 and in total more than 5,000 RACE machines were sold. The success of this machine is undoubtedly due to the fact that NSA bought the machine via its Merlin Procurement Agency and that it was adopted as a NATO machine. I don't know the reason why NSA bought the machine but it is likely they wanted a machine with a non-US crypto algorithm such as to not run the risk of revealing anything, even to NATO friends, about US crypto capabilities.

The development prototypes of RACE used the Norwegian developed microprocessor MIPROC developed at the Norwegian Defence Research Establishment, FFI - Forsvarets Forskningsinstitutt. This was a very advanced design for the time with both the data and address bus using 16 bits. The first versions of MIPROC was produced in Norway by the company AS Mikroelekronikk (AME) in Horten while later it was produced on an industrial scale by Plessey in UK. However, at STK, when the RACE was ready for industrial production they decided to switch to the newly released Intel processor 8080. RACE was a very robust machine and might very well be that some are still in use. It is known that the machine was used in Australia in 2002 as they then still ordered spare parts for the machine.

The battle with Aroflex for the NATO contract was very hard and in the end NATO decided to approve both of the machines. The machines were made interoperable but it is not entirely clear if the same crypto text could be deciphered on both machines or not. At least both machines adhered to the NATO standard APC 127 and produced similar formatted output. My personal guess is that they were also interoperable on the crypto level, but this has to be verified. The end result was that Aroflex won the European market while USA and their close partners preferred the more robust and better built RACE. As the crypto algorithm in RACE was software based it was relatively easy to adapt the machine for commercial use. The commercial version was called Cryptel 265 and was shown on telecommunication fairs all over the world, but the sales were poor especially due to the very strong competition in the commercial markets from the Swiss based Hagelin firm. I happen to have seen Cryptel 265 on the STK stand at the Telecom Exhibition in Geneva in 1983. I asked for a demonstration of the machine and I remember it was an impressive machine, which was extremely easy to use. Unfortunately the sales person did not allow me to take away the 5-level Telex tape that I had produced with copies of all the different test encryptions. Instead the tape went in the shredder.

As a curiosity, I can mention that the various software algorithms developed for RACE needed to be named to keep them apart and the developer team decided to use 5-letter names based on British horse tracks such as Epsom and Derby. Hence the name of the machine - RACE. Unfortunately they soon run out of names as there were not sufficient amount of British racing tracks with short, 5-letter names.

I don't know of any RACE or KL-51 manuals in public hands but one of the first production prototypes, SN/ 2, is in the collection of the Armed Forces Museum in Oslo, Forsvarsmuseet.  Unfortunately at that time I was not allied to open the machine.

I should like to mention that the information I have given here mainly is extracted from the Thales 50 Year Jubilee Book entitled: "Thales, On a Secret Mission - 50 years of Norwegian Cryptology", that was privately published in 2005 and with a few additions based on discussions and interviews with Norwegian cryptology experts. The definitive history will have to wait until further research can be done

STK, which was started in 1915 was taken over by ITT/Standard Electric in 1934 and it was part of this group until 1987 when ITT sold their shares to Alcatel which later became the Thales Group. Thales Norway is still manufacturing crypto equipment".

Ragnar Otterstad also comments.

"RACE/KL-51 equipment was originally developed by Lehmkuhl Electronics (I worked there early 1980s ).  The design was the brainchild of a former chief engineer of the Royal Norwegian Navy.  Upon retirement he started working for Lemkuhl in Oslo. He died some years ago.

The software was embedded in a chip manufactured in Southern California in cooperation with NSA, needless to say. A "civilian" version of RACE was also made and sold to various non-NATO countries. A portable version  was designated PACE.

Lehmkuhl was acquired by Elektrisk Bureau  AS, (LME) who later sold the crypto division to STK/ITT".

 Photo provided by David Smith

Photo provided by David Smith

This example is on display at the National Cryptologic Museum. (Photo by  Austin Mills , courtesy Wikipedia)

1) Frode Weierud <frode.weierud(at)gmail.com>
2) Ragnar Otterstad <la5he(at)yahoo.no>
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June 23/12