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Singlet   BID/60
Wheel-based cipher machine - wanted item

Singlet was a British electromechanical cipher machine that was developed and built in the UK in late 1949 or early 1950 as a replacement for the wartime Typex and the UK-version of the Combined Cipher Machine (CCM). The machine has 10 cipher wheels with 36 contacts each and is similar (but not identical) to the interoperable US KL-7. The machine is also known as BID/60. 1

The image on the right shows a Singlet machine after the dust cover has been removed [1]. At the front is a regular teleprinter keyboard with 29 keys and a space bar. At the rear is a removable cylindrical cage that contains the 10 electrical cipher wheels. At the front right is a paper tape reel on which the 5-bit output was punched.

The Singlet shows great resemblance to the American KL-7 machine, although the KL-7 has only 8 cipher wheels instead of 10. According to some reports however the wheels of the Singlet are identical to those of the KL-7 and Singlet could be made interoperable with the KL-7 by using just 8 cipher wheels and 2 dummies [3].

In 2005, a Singlet (BID/60) was on public display at Bletchley Park in the exhibition Enigma and Friends by David White and John Alexander.

According to the sign it had previously been in use at the Foreign and Commonwealth Office and was given on loan by GCHQ. This display has since been closed and as far as we know there is currently no Singlet on public display.
Singlet (BID/60) machine [1]

Another photograph was made by Kevin Coleman after the Singlet was removed from the display case [2]. It shows the machine with its dust cover in place and a blue box with the cipher wheels on top. Judging from this photograph, the wheels were indeed identical to those of the KL-7.

The blue storage case has room for 14 cipher wheels, indicating that the machine was possibly supplied with more than 10 cipher wheels. In that case, the key list would have dictated which wheels were to be used at any given date. According to surviving documents, Singlet was also used in Australia and New Zealand, but probably only for communication with the British Army.

  1. BID means British Inter Departmental. Systems with a BID designator are generally used by more than one single governmental agency or department. More...

Singlet (BID/60) [1]
Singlet (BID/60) [1]
Singlet (BID/60) [1]
Singlet (BID/60) [1]
Singlet (BID/60) with dust cover and blue box with 10 cipher wheels [2]

A complete Singlet machine is known as BID/60 and consists of the following basic components:

  • BID/60/1
    Base unit containing the keyboard, the mechanics and the electronic parts. This unit is similar (but not identical) to the KLB-7 (AFSAM 7/1) of the TSEC/KL-7.

  • BID/60/2 1
    Wheel stepping unit. This is the part that holds the rotor cage and controls the stepping of the wheels. It was probably a classified part of the machine. This unit is similar (but not identical) to the KLA-7 (AFSAM 7/2) of the TSEC/KL-7.

  • BID/60/3
    Removable cylindrical rotor tube (cage) with 10 cipher wheels. It can be removed by releasing the two large bolts in front of the cylinder. This unit is similar (but not identical) to the KLK-7 (AFSAM 7/3) of the TSEC/KL-7.
  1. The designator BID/60/2 has not yet been confirmed, but was probably used for the stepping unit.

Cipher wheels
Production process, by Bryan Targett

The cipher wheels of the Singlet are identical to those used with the American KL-7, which was introduced in 1952. The KL-7 was developed by the US National Security Agency (NSA) and it is quite possible that the wheels were a joint US/UK development, or that the Americans allowed the British to use their cipher wheels with Singlet. In any case, the Singlet wheels were manufactured in the UK by Egen Electric 1 on Canvey Island, as former employee Bryan Targett [4] recalls:

Right and left side of a KL-7 rotor

The image above shows a KL-7/Singlet wheel with the right hand side up, of which the spring-loaded contacts have been removed. The outer ring with the 36 numbers, was a die-casting for which a high-silicon aluminium alloy was used in order to obtain a very sharp molding. This was then anodised which, because of the alloy's silicon content, resulted in a black finish. The surface of the ring was then gently linished, which revealed the numers (1-36) in bright aluminium.

The centre part of the wheel is a thermosetting resin with the 36 flat-faced contacts of the left hand side, molded-in during manufacture. These contacts are made of Beryllium Copper (BeCu) and the plastic surface was also linished to remove any molding flash and expose the contacts.

Spring loaded contact

The other side of the centre plastic part carried the 36 spring-loaded contacts, or plungers, by which the signal was transferred to the adjacent wheel. Each plunger consisted of an outer Beryllium Copper body containing a spring with a contact disc fitted at one side. The spring was soldered into the plunger body by means of an automated system which inserted a small piece of solder into the body, followed by the spring assembly. This was then heated using RF induction.

Plunger construction detail

The plunger body needed to be heat treated before assembly, which involved heating to around 300°C in an Argon atmosphere in order to minimise oxidation of the Beryllium Copper. To ensure that any oxide that may have occurred was completely removed, the plungers were chemically cleaned before assembly. These plunger assemblies fitted into the 36 holes of the plastic disc that is visible in the photograph above. A random sample from each heat treated and cleaned batch was tested for Vickers hardness, a 1921 method to measure the hardness of materials [5].

The units were assembled by female workers on a production line of special machines, some of which were made internally, whilst others were purpose-built externally by sub-contractors. At the time, Egen Electric was just a subcontractor for certain parts of the Singlet cipher machine. The machine itself was manufactured somewhere else and was never seen by Egen personnel. Even the wiring was done elsewhere, most likely in a government facility in Blackburn (Lancashire, UK) [4]. The only contact which the Egen personnel had, was with the AID 2 ministry inspectors. Like the wiring of the KL-7 wheels, the wiring of the Singlet wheels is currently unknown.

  1. At the time, Egen Electric Ltd. on Canvey Island was a subsidary of the Philips/Mullard consortium. Between 1961 and 1965, Bryan Targett [4] was the (only) Chief Chemist at the Egen factory and as such he was reponsible for the production process and quality assurance of the Singlet cipher wheels.
  2. AID = Army Inspection Department (UK).

  1. Matt Russell (Crypto Matt), Images of Singlet BID/60
    Bletchley Park, 27 May 2005. Via Wikipedia. Retrieved March 2015.

  2. Kevin Coleman, Image of Singlet BID/60 with storage case and rotors in box
    Bletchley Park, 2005. Personal correspondence. Retrieved March 2015.

  3. Mike Simpson, BID/60 (Singlet)
    Jerry Proc's crypto pages. Retrieved march 2015.

  4. Bryan Targett, Description of the cipher wheel production process
    Crypto Museum. Personal correspondence, March 2015.

  5. Wikipedia, Vickers hardness test
    Retrieved March 2015.
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Crypto Museum. Created: Saturday 14 March 2015. Last changed: Sunday, 11 April 2021 - 16:39 CET.
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