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
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 . At the front is a regular teleprinter keyboard
with 29 keys and a space bar. At the rear is a removable
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
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 .
In 2005, a Singlet (BID/60) was on public display at Bletchley Park
in the exhibition Enigma and Friends by David White and John
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.
was made by Kevin Coleman after the Singlet
was removed from the display case . 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
BID means British Inter Departmental. Systems with a BID designator are
generally used by more than one single governmental agency or department.
A complete Singlet machine is known as BID/60 and consists of the following basic components:
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
- 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
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
The designator BID/60/2 has not yet been confirmed, but was probably used
for the stepping unit.
Production process, by Bryan Targett
The cipher wheels of the Singlet are identical to those used with the
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  recalls:
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.
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.
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 .
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) .
The only contact which the Egen personnel had, was with the AID 2 ministry
Like the wiring of the KL-7 wheels, the wiring of the Singlet wheels is
At the time, Egen Electric Ltd. on Canvey Island was a subsidary of the
consortium. Between 1961 and 1965, Bryan Targett  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.
AID = Army Inspection Department (UK).
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© Crypto Museum. Created: Saturday 14 March 2015. Last changed: Sunday, 11 April 2021 - 16:39 CET.