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UK KL-7 →
Rotor-based cipher machine
- wanted item
Singlet was a British
rotor-based 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 rotors with 36 contacts each,
and is similar (but not identical) to the interoperable American
KL-7.
The machine is also known as BID/60. 1
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The image on the right shows a Singlet machine of which 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
with 10 electrical cipher rotors. At the front right
is a reel with paper tape into which the 5-bit output was punched.
Singlet (BID/60) shows great resemblance to the American
KL-7 machine,
although the KL-7 has only 8 cipher rotors
instead of 10.
According to some reports however the rotors 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 rotors 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.
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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 rotors on top.
Judging from this photograph, the rotors were indeed identical to those
of the KL-7.
The blue storage case has room for 14 cipher rotors, indicating that
the machine was possibly supplied with more than 10 cipher rotors.
In that case, the key list would have specified which rotors
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.
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BID means British Inter Departmental. Systems with a BID designator are
generally used by more than one governmental agency or department.
More...
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A complete Singlet machine is known as BID/60 and consists of the following basic components:
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- 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
Rotor stepping unit. 1 This is the part that holds the rotor cage and controls
the stepping of the rotors. 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 rotors.
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.
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The designator BID/60/2 has not yet been confirmed, but was probably used
for the stepping unit.
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Production process, by Bryan Targett
The cipher rotors 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
rotors were a joint US/UK development, or that the Americans allowed the
British to use their cipher rotors with Singlet.
In any case, the Singlet rotors were manufactured in the UK
by Egen Electric 1 on Canvey Island,
as former employee Bryan Targett [4] recalls:
The image above shows a KL-7/Singlet rotor 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 rotor 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.
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 rotor. 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.
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 rotors, the wiring of the Singlet rotors is
currently unknown.
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At the time, Egen Electric Ltd. on Canvey Island was a subsidary of
Cambridge-based Pye, for which it manufactured electronic components [6].
Pye was later taken over by Philips (1967-1986) [7].
Between 1961 and 1965, Bryan Targett [4] was the (only) Chief Chemist
at the Egen factory. He was reponsible for the production
process and quality assurance of the Singlet cipher rotors.
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AID = Army Inspection Department (UK).
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- Matt Russell (Crypto Matt), Images of Singlet BID/60
Bletchley Park, 27 May 2005. Via Wikipedia. Retrieved March 2015.
- Kevin Coleman, Image of Singlet BID/60 with storage case and rotors in box
Bletchley Park, 2005. Personal correspondence. Retrieved March 2015.
- Mike Simpson, BID/60 (Singlet)
Jerry Proc's crypto pages. Accessed March 2015.
- Bryan Targett, Description of the cipher rotor production process
Crypto Museum. Personal correspondence, March 2015.
- Wikipedia, Vickers hardness test
Accessed March 2015.
- Pye Story, Egen Electric
The Pye History Trust, 2026. Accessed 15 June 2026.
- Pye Story, History, Acquisition by Philips
The Pye History Trust, 2026. Accessed 15 June 2026.
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© Crypto Museum. Created: Saturday 14 March 2015. Last changed: Monday, 15 June 2026 - 07:01 CET.
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![Singlet (BID/60) machine [1]](img/302060/000/full.jpg)
![Singlet (BID/60) [1]](img/302060/001/full.jpg)
![Singlet (BID/60) [1]](img/302060/002/full.jpg)
![Singlet (BID/60) [1]](img/302060/003/full.jpg)
![Singlet (BID/60) with dust cover and blue box with 10 cipher rotors [2]](img/302060/004/full.jpg)
