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OTT UK Rockex →
One-time tape online cipher machine
- not in collection
5-UCO, also known as HST and as BID/30, 1
was an electronic One-Time Tape
(OTT) cipher machine,
or mixer, developed in the UK
during WWII and used for Top Secret Ultra
messages during the war. After the war, the machine was used by the
British Commonwealth 2 , the US and NATO.
The machine was suitable for fully synchronous secure
teleprinter traffic over HF radio bands.
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5-UCO was an extremely large machine that consisted of a 6-foot tall 19"
rack in the which the various electric, electronic and mechanical parts
were mounted, plus an external teleprinter.
5-UCO is the abbreviation of 5-Unit Code, 3
indicating that it was intended for 5-bit teletype circuits. It provided
full Traffic-Flow Security (TFS) and could be operated over (commercial)
land lines as well as over noisy HF radio links.
The machine is driven by a central 160V DC motor that is mounted at
the centre. Next to it are two readers for perforated tape: one for the
transmission key tape and one for the reception key tape.
An additional DC motor is mounted to the rear of the receiving tape reader.
It is part of a phased-locked loop synchronisation system.
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The image above shows a complete BID/30/1 setup. At the left
is the 19" rack that contains the 5-UCO device.
It is connected to the teleprinter
that is placed on the table at the right [1].
The image was provided by GCHQ and is reproduced here with kind
permission from Director GCHQ.
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5-UCO was developed during WWII, in or around 1943, by Colonel G. ff Bellairs,
Dr. G. Timms and Mr. D.C. Harwood [4].
During the war it was used for distributing
Ultra Intelligence
to commanders in the field without the risk of any messages
being decrypted by the enemy. After the war it was kept in use
for several years, also by US Intelligence Agencies, because of its
synchronisation capabilities, its TFS function,
and its ability to be used in tandem over narrowband HF radio links.
Despite its capabilities, the system was only used for traffic at the highest
classification level, mainly because of its high operational cost.
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In 1955, the price for a single 5-UCO was USD 12,000, 4
whilst the machine was permanently in short supply [7].
In 1960 it was estimated that the key tape supply cost GBP 5,000 per year
for a single 5-UCO machine [2].
In the mid-1960s, the 5-UCO (BID/30) was therefore gruadually
replaced by the NSA-developed
TSEC/KW-26 stream cipher
(codenamed Romulus and Orion).
Customers who needed to stay with one-time tape,
had a choice between ETCRRM and
Ecolex II.
The 5-UCO was so secret, that it was initially thought that all machines
had been destroyed when they were decommissioned in the second half of
the 1960s. However, in 2018 a nearly complete UCO-5 (BID/30/1) was
discovered in the vaults of GCHQ. The machine was on public display
the following year, at the temporary exhibition
Top Secret: From Ciphers to Cyber Security
at the Science Museum in London (UK).
The photographs below were made there in November 2019.
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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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In this context, the expression 'British Commonwealth' is used to
identify the following countries of the Commonwealth of Nations:
Great Britain, Canada, Australia and New Zealand.
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According to some sources, 5-UCO is the abbreviation of
5-Unit Controlled. The accounts differ. Note that
different users/services used different names for the device.
➤ More
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In the 1953 NSA Cipher Catalogue [12], the 5-UCO is listed for a
unit price of GBP 2,500 — the equivalent of USD 7,025 in 1953.
In 1955, the same machine was offered to NATO members for USD 12,000 [7].
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Unless stated otherwise, the images above are Copyright Crypto Museum (2019)
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The image below is probably the only one of its kind that has survived [1].
It shows a complete BID/30/1 setup at the left, connected to an external
Creed 7 teleprinter on the table at the right.
The BID/30 unit (5-UCO) consists of
the 6-feet tall 19" rack on the left, divided into 9 sections,
numbered from top to bottom 1A to 9A (printed on the right vertical
bar of the rack). Note the presence of a morse key
on unit 6A. It was used for clear communication with the other end.
The rear of the rack (only partly visible here) also holds several modules,
numbered 1B to 7B.
The machine is mechanically driven by a 160V DC motor (6A) that has two
additional windings: one known as the advance winding and the other
one known as the retard winding. To the right of the motor are two
Creed 6S tape readers and some
mechanical gears. The central motor drives the TX keytape reader
and — through a differential gear — the RX keytape reader
at the right.
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Just above the Power Supply Unit (8A and 9A) is an alarm bell (7A)
that went off if one of the sensing pins in the TX tape reader got stuck [5].
Operators then had to repair the unit before continuing. This operation
was checked daily by means of a test tape that simulated the problem.
On the control panel (5A), between the large meters, are 4 indicator lamps:
2 red and 2 green ones. Two lamps flashed when the receiver's
advance/retard motor was activated, whilst the other two stayed on to show
whether the last correction was advance or retard.
Under normal conditions the lamps alternated randomly.
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When the pattern changed however, it was an indication to the operator
that the machine at the other end was running too slow or too fast, in
which case the operator had to use the T-bar to make corrections [5].
The image above shows a close-up of unit 6A, which holds the motor
(left) and the two Creed tape readers.
The differential gear with the
T-bar for manual advance/retard correction is visible in between the
tape readers. To its right is a regular morse key,
which is used for clear communication with the other end.
Move the mouse over the image to highlight it.
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At the centre of the machine, just under the control panel,
are two Creed 6S6 tape readers
that accept standard 5-hole paper tape.
The leftmost reader is for the plaintext tape, whilst the rightmost
one must be loaded with the keytape.
Both tape readers are engraved with the text '7 UNIT'. This refers to the
serial data word format, which is
7 bits wide (1 start bit, 5 data bits and 1 stop bit).
Note that is different from regular tape readers which
support 7½-bit data words (7½ UNIT) with
1 start bit, 5 data bits, 1½ stop bit.
➤ Creed 6S6 tape reader documentation
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In the years following WWII, the alliance of West-European states,
known as the Western Union (WU), used a number of British and American
cipher machines for secure communication beteen the member states.
This situation continued after the WU was dissolved into the
North Atlantic Treaty Organisaton (NATO)
in 1949. Typex machines
were used on the links between NATO headquarters and the UK,
whilst CCM machines were
used for communication between the other member states and NATO.
However, these machines were not approved for TOP SECRET traffic.
For traffic at the highest level of classification, NATO used
the American SIGTOT
and the British 5-UCO, but both were permanently
in short supply [6].
Furthermore, the 5-UCO was considered too large to
be of practical use in the field, not to mention the high price of
US$ 12,000 [7].
This situation changed when in 1953 first the
Norwegian ETCRRM
was developed and later the Dutch Ecolex.
Both machines were approved
for COSMIC and NATO messages of all classifications in 1954
and would soon replace the 5-UCO and SIGTOT machines.
The price of these machines was also a bit lower:
US$ 3,000 for the Ecolex II
and just US$ 1,200 for the ETCRRM
[7].
➤ More about NATO
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Like most other cipher machines in the
mixer class, 5-UCO uses
the so-called Vernam Cipher,
a method of 'mixing' the plaintext character-by-characcter with
characters from a random-key tape,
using a binary XOR operation (modulo-2 addition). At the receiving end,
the same random character from an identical key tape was mixed with
the encrypted character, revealing the original plaintext character.
If the characters on the key tape are truely random, and only two
identical key tapes exist (which are used only once and are destroyed
immediately after use), this code can't be broken.
It is the only method for keeping a message secret indefinitely.
➤ More about one-time tape cipher machines
➤ More about the Vernam Cipher
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In order to keep the machine 'in sync' with the station at the other end,
a crystal-controlled timebase is used. The signal from the crystal oscillator
at the top (1A) is fed to a divider circuit (2A) and then to a phase
comparator (3A) where it is synchronised with the signal from the sprocket
wheel of the TX tape transport system. The output of the phase comparator is
used to drive either the advance or retard windings of the
central motor, as illustrated in this drawing:
An additional small reversible DC motor was mounted to the rear of the
rightmost tape reader. Through the differential gear, this motor automatically
kept the data stream synchronised with the distant station. A T-bar,
mounted in between the two tape readers, also allowed manual advance/retard
correction. This was needed during the startup of a session or after the
signal was lost due to bad HF conditions. Once it was manually synchronised,
the timebase took over.
In transmission mode (TX), the signal from the main teleprinter hall
(or an individual teletype unit) arrives at the 5-UCO where it activates
the start/stop clutch and engages the TX keytape reader. The 5-bit teletype
signal is then 'mixed' with the 5-bit data from the tape reader (XOR) and
converted to a serialised data stream that is subsequently transmitted,
as shown above.
In receiving mode (RX), the process is reversed. The incoming signal
is used to synchronise the timebase, which in turn controls the
speed of the RX keytape reader. The received serial data stream is
then converted to 5-bit code and mixed with the 5-bit data from the
tape reader (XOR), which is then serialised again and delivered to
the connected teleprinter, as shown above.
To maintain synchronisation, the tapes were running constantly,
even if no data was actually sent. This is known as Traffic Flow Security
(TFS).
In such cases, the all-spaces character was constantly encrypted
and sent. As the key tape lasted ~ 3 hours, it was important to
use it as efficiently as possible. For this reason, messages were generally
not entered directly on the teleprinter, but on a punched paper
tape which was prepared in advance of the actual transmission.
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TEMPEST is a US/NATO acronym for (the study of) intelligence-bearing
emanations that can lead to loss of security of a cipher system. In other words:
information can 'leak out' from the device, allowing a malicious party to reconstruct
(part of) the plaintext of an encrypted message. This phenomenon was first
discovered during WWII, in 1943, by Bell Labs engineers
in the US, and affected nearly all electric/electronic ciphermachines.
Information can leak from a device in various ways, including acoustic, optical,
inductive and via RF radio waves (radio interference).
Apparently, the 5-UCO was no exception to the rule, as in the internal
NSA Cipher Catalogue
of 1953 [12], the following is written about the machine
on page 59:
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Radiation: The equipment is inherently insecure and it must
be assumed that security is compromised by radiation.
Remedial measures would involve re-design.
For a long time, TEMPEST was a secret field of research, that was not
shared with other countries. It became known in the rest of the world between
1959 and 1956, but in 1953 most countries were not aware of the risks.
There are several possible remedies, including shielding of the circuits,
filtering of power and data lines, and defining a mandatory distance
from the equipment.
It is clear from the above note, that 5-UCO's TEMPEST could not be fixed
without a redesign. With its 'open rack' architecture and unshielded circuits,
the machine was 'one big antenna'. It is likely that in practice, the TEMPEST
problems were 'fixed' by adding filters to the power and data lines, and by
defining a minimum distance for unauthorised personnel.
➤ More about TEMPEST
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My recollections of BID/30
8 April 2015 [5]
The equipment was rack mounted and about 6 ft high.
At the centre, there was a sealed gearbox driven by a 160V/DC motor.
It had 2 extra windings: advance and retard.
External to the gearbox and rear-mounted were
3 distributors, a toothed wheel and a small DC motor.
Front mounted were two Creed 6S6 auto heads,
and a manual advance/retard handle in the form of a T-bar.
A crystal oscillator and divider circuit fed a phase comparator;
the other input was from the toothed wheel pick-off coil.
The output was fed to either the advance or retard winding and so locked
the motor speed and transmit random key tape to the crystal reference.
Through a differential gear the motor also drove the receive random key
tape auto head. This was kept in sync with the distant terminal, automatically
by a small reversible motor, or during set up/lost sync by the manual
advance/retard handle.
Asynchronous 7½-unit baudot from teleprinter or auto head in traffic
hall was fed via a clutch to the start/stop distributor.
This routed the 5 code elements to 5 storage capacitors.
Each bit was added modulo 2 to the key bit.
The synchronous transmit distributor re-assembled this as a serial
7-unit cipher output. In the absence of traffic the "all space" character
was enciphered.
Incoming receive cipher reversed this process and fed plain text to local
or distant teleprinter or printing reperforator. An "all space trap" sent
steady mark output. If the incoming element changeovers were out of step
with the key tape element changeovers then the auto advance/retard motor
would correct this error. Red and green lights showed advance or retard
in progress (flashing when motor operated) and (steady light),
the last operation.
During start up, a half turn on the manual advance/retard changed the key
one character. If the equipment lost sync after an outage, then the handle
was pulled out, rotated slowly to find the "in sync", indicated by
plain text or mark on the local teleprinter.
It was then dropped into the nearest element detent.
Key tapes lasted about 3 hours and were destroyed after use.
We learnt to remove them from the single sided spool and tear the tape
in one operation. New boys usually failed their first attempts and ended
up unwinding them into the waste sack!
The start/stop distributor, DS1, was quite noisy and when the traffic
hall did its finals at 23:59, the clatter from a row of BIDs would awake
any technician grabbing 40 winks.
Alarm circuits monitored for stuck peckers on the transmit auto head.
These were checked daily with a test tape. Faults were usually polarized
relays needing adjustment and dirty distributors or worn brushes.
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Looking for a machine called HST
22 June 2014 [8]
I was trained as an Electronic Technician (Cipher Mechanic) in 1953 and
worked on two machines that I have never subsequently seen or heard mentioned.
One was called ROCKEX and was a free-standing unit utilising a
bank of thyratron electronic valves and the other was a large fixed
electronic unit utilising one-time perforated tape for encryption on
a high-speed telegraphic link to war office command HQs around the world.
It was called HST.
The HST machine transmitted encrypted messages in real time between
continents, and used a one-time perforated tape that had to be synchronised
with the machine at the other end.
It was a vertical stacked machine, about 5 ft high,
with modular racks of pentodes etc., and a type of handle on the front that
enabled the operator to sync the tape (on the front of the machine) manually
with the receiving unit. We were told that there were only ever 2 random tapes
manufactured: one held in London and the other
mailed out to the particular foreign station.
I used this machine at GHQ Nairobi Cipher Office from 1954-1956 to transmit
to London, Melbourne, Singapore, Aden, etc., and handled topsec traffic
re: Archbischop Makarios detention and also the Suez fiasco, etc.
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We received the above story by e-mail from Anthony (Tony) Bellchambers
on 22 June 2014. Although we were able to help him with information about
Rockex, we had no idea about the other machine, which he called HST.
After reading his description again, we figured that he might be talking
about the 5-UCO of which we had just received a photograph from GCHQ.
After sending him the photograph — this page did not yet exist — he confirmed
that it was indeed the one we was talking about: BID/30.
In March 2015, after this page had come online, he replied:
Yes, that is indeed the machine. Very many thanks! It certainly rolled back
the years to the hours I spent trying to find which valve in the frequency
divider was faulty!
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Looking for a machine called 'racks'
5 January 2017 [9]
When I was in the Royal Navy, in 1962, I was at the Naval Base HMS Jaffair
in Bahrain, where we used a cipher machine that was called,
I think, "racks". Basically there were stocks of reels which consisted of
5-unit tape and I, at the sending station, would take a reel from stock,
put it on the rack and put the start of the tape (blue line I think)
on an auto head (probably a Creed).
The receiving station would have the same tape and he would put it on the
same position as me. Then, the initiating party (in this case me) would send the
word mark plus a letter in morse code,
then a long dah (also in morse code), and then we would both start
the tape together.
Its a long time ago and I hope I have got it right,
but my question is "do you have any information about it?
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After replying that he might be looking for the 5-UCO (BID/30),
we received the following response:
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It is indeed the 5-UCO (BID 30) machine. I have looked at Richard P.'s
web page [3] and noticed the BID 30 Start sequence, which is what I was after
in terms of using the morse key.
However, I am a bit unsure of the QRV part shown in 2, 3, 4 and 5 on both
Station A and Station B, as I thought I used to send the word 'mark'
in morse (-- .- .-. -.-) which, if you run that together, would be QRK.
Otherwise everything else is correct.
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BID/30 Start Sequence |
Station A | Station B |
- With gate open and auto head running, 'Start Space' characters will be sent.
- On receiving '
QRV ', switch auto head to 'Stop'. Align send tape on agreed mark. Close gate. - Switch to Start. There will be 3 'Dahs' and auto head will run.
- Await Station B '
QRV '.
- When '
QRV ' received, send 'K' and await 3 'Dahs'.
| - Pull out advance/retart handle, rotate until meter shows 'Mark'. Align tape on receive auto head with it switched OFF. Close gate.
- Send '
QRV ' on morse key.
- 3 'Dahs' will be heard.
- On end of 3rd 'Dah', switch auto head to run. If in-sync, then meter will show 'Mark'. If not, then rotate 'advance' 180 degrees, one character, until 'Mark' is seen.
- Prepare transmit and send '
QRV '.
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BID/30 Start Sequence courtesy Richard P. [3][5].
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Recollections of the HST
24 January 2022 [11]
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In the story below, Ken Elks refers to the 5-UCO by the name HST.
Our comments are in square brackets [...].
The HST machines — the name we were given when we trained on the at 1TR,
Catterick — were universally known as 7-UCO in the field.
The teleprinters of the 1950s were limited in what could
be printed, because they only used 5 units (bits).
This meant that apart from the 26 letters, there were only
four other functions possibe (codes 00000 and 11111 were special use).
These were carriage return (CR), line feed (LF) and shift keys (LTR, FIG),
used to print letters and numbers.
Each 5-bit code was automatically prefixed by what we referred to as
a start space and a stop mark, to indicate the start and finish of each
letter [as illustrated above]. To make certain that the end of the letter was recognised, the
stop mark was lengthened in time by 50% [i.e. 1½ unit].
The result was called 7½ a half UCO.
The idea behind the HST was that they ran continously. whether a message
was being sent or not. [Today, this feature is known as
Traffic Flow Security or TFS].
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Part of the security of such machines is that they should hide the start
and finish of each letter, and to do this there was a wipe on, wipe off
device on the back of the machine, which converted the 7½ units to the
equivalent of 7 units, hence the name 7-UCO.
This converter was one of the least reliable parts of the machines,
and constantly needed to be adjusted and set up.
When the messages were decoded at the other end, the stopmark was
extended back to 7½, so that it would work with a regular teleprinter.
The name 7-UCO did not mean that 7 bits were used to describe a
character – that was for later equipment – it merely refers to the
data format.
The incoming signal from the tape readers was wiped on to the outer
segments (to take the 7½) and wiped off by the inner to give 7UCO.
The ends of the arms held carbon brushes to make electrical contact.
When a message was being sent by tape reader, these arms rotated
continuously. But when using a teleprinter, the rotation was quicker
than you could type so the arms kept stopping and starting again
all the time.
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As you can see, it is all held together by nuts, bolts and screws,
and this was the weakness. The stress when it stopped, gradually loosened
the fixings, and the whole thing more or less started to fall apart.
Also, the brushes were held against the rings by springs, and when the
arms became loose, these springs pushed the arms up. Instead of
making proper contact, it would miss digits.
Although the voltage was low, this could also cause arcing and there are
signs of this on the rings. The rectangular pieces between the segments
were not connected to anything, but were present to make sure the brushes
did not bridge two segments.
They were also made of brass to keep wear even.
One of the maintenance jobs entailed using a pencil of glass fibres
to clean out the accumulation of carbon between these separators
and the segments. This had to be done on a weekly basis.
If you couldn't find the "pencil", a screwdriver blade did the trick,
but could cause damage and was avoided if possible.
One of the difficulties I experienced was that e/techs were prone to
"finger" trouble, causing additional faults when trying to clear up
a previous one.
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The purpose of some of the parts is explicable when you know how the tapes
were handled. Each tape lasted four hours.
When it ran out, the machine stopped automatically to prevent messages
going out in clear.
We would get the next tape from the rack and, with a
teleprinter, we checked with mech at the other end the
last three digits of its number, to make sure we each had the right one.
Each tape was marked by a series of printed bars, each numbered,
starting with 1.
The tape was fed through the tape reader on the front of the machine and
fixed through a slot on the other spool, then wound through by hand,
until the first bar was in the reader.
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We closed the latch on the reader, then set it to start.
It gave three warning beeps after which it started automatically.
At the receiving end, the tape was started on hearing the third beep.
The speaker for this is at the top of the machine on the right [1A];
you can see its circular shape.
A transmission could be initiated from either end, but in
most cases it was done from the UK end.
Setting up random tapes had to be done for each direction, so that
there was an outgoing tape (on the left) that you initiated and the
receiver had to synchronise with, and one received (on the right)
which you had to synchronise with.
The labelled handle [i.e. the T-bar] between the two tape readers
in the photo [see below] is the one that is used for this receiver
synchronisation.
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Just above the tape reader is a meter. When the two machines were
synchronised, the needle on this meter was steady, but if not
synchronised, it flickered about. The recipient then turned the
T-bar on the gearbox to bring the two machines in-sync:
one complete turn to advance or go back one letter,
or one notch for a single bit.
When all was OK, you sent the letter R,
tapped out on the morse key [visible in the image just above
the T-bar],
and then, if on nights, went back to sleep!
If for some reason there was a breakdown part way through a tape,
you had to restart the message from the next available bar.
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After you had done this a few times it was quite normal to get the
timing exactly right, and didn't really have to do much to synchronise.
WIM, HST and ROCKEX all used the same type of random tapes,
but because of the need for both sender and receiver to use the
same tapes, they were always allocated and kept separate.
HSTs used at least six tapes a day, and therefore over 4,000
a year per machine (and we had five of them).
Every morning when coming off the night-shift, we had to collect
all the used tapes, and bring them to the incinerator to have them
destroyed.
One of the secrets, especially on night-shifts, was to ensure that
the tapes on all machines didn't runout at the same time,
as there was usually only you to deal with them.
On the other hand, you didn't want this to happen randomly,
so the first thing we did when going on shift at 11:00 pm, was
to restart all the machines with fresh tapes, discarding anything that
was part used.
That way you could safely have a three-hour nap,
unless there was something that needed attention.
Most of our ROCKEX traffic [another
one-time tape machine]
was actually sent or received as encrypted messages over HST,
which means that it was doubly enciphered.
The reason for this is that the content was so secret, that they didn't
want any operator along the way to read them.
The problem with using HST for transmission, was that any mistake
in what was received, could throw the decryption out-of-sync, because
of the stunt and shift characters.
If there was a problem, the message
had to be sent again, but this was frowned on because of the security
risk involved. For security reasons a re-transmission had to be done
with a fresh keytape.
I think seeing an HST machine today would be like meeting an old friend again.
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In the above text, Ken Elks suggests that the three machines —
WIM, HST and ROCKEX — all used the same keytapes. We are not
certain wether this is indeed the case, since ROCKEX uses a
6-hole keytape, rather than 5-hole.
7 July 2019 [11]
I have just read an interesting book: GCHQ, The Secret Wireless War
1900 to 1986 by Nigel West. Having just read it, I was disappointed not
to read anything about what I have been involved in. So
I just put "Electronic BID/30" into Google and your page appeared with,
surprise, surprise ... a BID/30 Machine. How interesting. I have not seen
anything like this since 1959 to 1961!
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Looking around your excellent Web Site, I found documentation which indicates
I can now talk about what I did between June 1959 and February 1961.
I was a 2nd Lt in the Army, REME at Arborfield, near Reading and was
in-charge of Training of Cipher, Wireless and Land Communications.
I was a National Service man, the last of that breed as it was running
down after WWII.
I am pleased you said the BID/30 in the photo was old because mine looked
similar but not the same. I simply cannot remember how many I had — I think
it was 8 but it could have been more. They were erected on each side of the
laboratory to pretend the other one was miles away. I also had other
Cipher equipments but that is another story.
Bye the bye, I never heard it called 5-UCO.
What I remember was two strips of standard Post Office Alarm type fuses
towards the top of the rack. Everything went through these fuses which
were rated very critically; too critical in my view.
I remember somebody saying that they thought one of these racks caught
fire at some time and the fusing then did not blow - so this panel was
introduced. Trouble was the fuse often blew for what seemed no reason
whatsoever.
So my Sergeant and I introduced a day
whereby we blew all the fuses in sequence to let the students know what
the effect was on the equipment.
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It went down like a storm throughout the World and we got a lot of
'brownie points' from doing this.
They were Alarm fuses which show a little tab when they blow
- as they also put another little tab onto the alarm Bus-Bar below.
Trouble was that occasionally the visual indication was so slight you
could easily miss it (unless you were standing on a stool or small ladder
and looking very carefully or running your finger along) without causing
another one to blow then as well!.
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I suggested to slightly increase the value of some of the fuses,
but this was stamped on from the War Office as something terrible.
I could have done with your lovely diagrams back then, but I have not
seen these, as far as I remember.
It was a complicated beast to get to work normally; never mind finding
what had gone wrong when it did not work. Problem being in real life: it
need not have been your machine, but the one miles away, or even in a
different country.
Fuses of this type were used with the BID/30 →
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I also worked as a British Post Office
Technician in Army Boddington
(Centre of Army Communications for the World), where they had BID/30s.
However, I never saw them there.
I also worked at the GCHQ in Cheltenham, where I watched
them packing up the BID/30 One-Time Tapes,
which were then distributed around the World.
At that time I never let on I knew what they were doing!
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Funnily, when I left the Army, I had a month holiday with pay, but I got
so bored, that I re-joined the Post Office Telephones.
I was subsequently sent to Boddington, where I met six students I had
lectured two months before. At that occasion I was not involved with Cipher,
but with the teleprinter side of comms.
I was at Boddington when the Army transferred it to the RAF.
Still there, but currently owned by GCHQ.
The photograph you have from GCHQ of the BID/30;
shows a Creed 7
sitting on a Standard DTN Table. These were standard
issue for the Defence Telegraph Network, which ran all around the UK
during WWII. They were designed to be sturdy to take the weight of a couple of
Creed 7s, or a Creed 7
and a tape machine.
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1959 to 1961 were very happy days for me then. I was also in charge of the
Amateur Radio Station, G3IHH, which is now no longer —
in fact the whole site is a Business Park now.
A past friend, Geoff Mills, used to work at the GPO Headquarters with
Tommy Flowers in the early 1950s.
They produced the Register Translator Mark II, 1 which was installed
in Bristol, and used on the first Electrical Subscriber Trunk Dialling (STD)
between Bristol and Scotland. It was opened in 1958 by Queen Elizabeth II.
Several years later it became known that Flowers
had been involved with Bletchley Park during WWII, after which
Geoff realised that the Register Translator 1 was in fact a
variation from Colossus.
Between 1970 and 1982, I was involved in updating the Register Translator Mark III
to cope with the introduction of International Direct Dialling (IDD).
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A Register Translator (RT) was used in old telephone exchanges.
When someone dialed a number, e.g. 1245 Chelmsford, the customer was
allocated a Register, which then occupied the Translater
for a couple of seconds. The Translator, which knew how to route
the call throughout the country, passed its information to the Register,
which then used it to complete the call. The Translater would then
proceed to the next caller, and so on.
An average exchange had two such Translators in those days.
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Device One-Time Tape cipher machine (mixer) Purpose Secure military and diplomatic communications Name HST Model 5-UCO, 7-UCO Designator BID/30 Developers Col. G. ff Bellairs, Dr. G. Timms, Mr D.C. Harwood Manufacturer ? Year 1943 ~ Country UK Users UK, USA, Canada, Australia, New Zealand Successor KW-26, ETCRRM, Ecolex II TFS yes Alphabet ITA-2 Tempest Insecure Dimensions (HWD) 1830 × 485 × 485 mm Weight 205 kg Quantity ? Price USD 12,000 (1955) [7] Cost GBP 5,000/y (1960)
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BID/30 1943 Initial version BID/30/1 1953 Improved TFS [12]
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The machine is known by the following names:
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HST High-Speed Telegraphy 5-UCO 5 Unit Code 7-UCO 7 Unit Code BID/30 British Interdepartmental 30 BID/30/1 Same, but Revision 1
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It is likely that the official name of the machine is HST, which was
the name it was known by in the user community.
The name 5-UCO, also written as 5 UCO or 5UCO, refers to the
number of encrypted bits (5 Unit Code), and was probably used by
technicians [5][8].
Technicians also used the name 7-UCO, since that is the
format of a serial data word 1
(1 start bit, 5 data bits and 1 stop bit).
The name 'HST' has been confirmed by two sources [8][10].
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Actually the word length of a teleprinter signal is 7½ bits, but the
HST converts it from 7½ to 7 bits before encryption, and then back
to 7½ bits again before transmission.
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1A Crystal oscillator 2A Clock divider chain 3A Phase comparator 4A Relay section 5A Controls and readouts 6A Main motor and tape readers 7A Alarm bell 8A Fuses and power distribution 9A 0/80/160V DC PSU
1B ? 2B ? 3B ? 4B ? 5B Commutators & DC motor 6B ? 7B ?
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- GCHQ, Photograph of complete BID/30/1 (5-UCO) machine
Photographs kindly supplied by GCHQ and
reproduced here with kind permission from Director GCHQ.
3 December 2012. Crown Copyright.
- Jerry Proc, BID 30/5-UCO (5-Unit Controlled)
Accessed March 2015.
- Richard P. (anonymous contributor), BID 30, (5UCO) Mechanical Detail
Jerry Proc's crypto pages (website) [2]. Retrieved March 2015.
- The National Archives,
Awards to civilian personnel in respect of cypher machine development
AVIA 65-977. Original reference: JY/808/01. 1955-1960.
- Richard P. (anonymous), My recollections of BID/30 (HST, 5-UCO)
Personal correspondence, 8 April 2015.
- NATO/ACCA, On-Line Cipher Equipments
SGM-279-54. 29 March 1954. NATO SECRET.
Declassified by NATO in 2006 (IMSM-0001-2006).
- NATO, Automatic Crypto-Equipment Requirements for the Allied Command Atlantic
SGM-560-55. 15 August 1955. NATO SECRET.
Declassified by NATO on 24 November 1999 (IMSM-0431-99).
- Anthony (Tony) Bellchambers, Looking for a machine called HST
Personal correspondence, 22 June 2014.
- John Youde (G0GUF), RNARS 32271, Looking for a large machine called 'racks'
Personal corresondence, 2-5 January 2017.
- Ken Elks, Recollections of the HST
Personal correspondence, 22 January 2022 - 21 February 2022.
- John Bowen (G8DET), Remembering the BID/30
Personal correspondence, 7 July 2019.
- NSA Catalog of US and UK cipher equipment - 1953
Cifax, Offline Literal Crypto Systems, Teletype Online Crypto Systems and Ciphony.
LCS(53)/N/R. NSA, 1953.
p. 59 (PDF p. 64)
Friedman Archive. Declassified by NSA 2014-06-11 (E.O. 13526).
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© Crypto Museum. Created: Friday 13 March 2015. Last changed: Friday, 21 August 2026 - 20:19 CET.
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![Image provided by GCHQ and reproduced here with kind permission from Director GCHQ [1]. Crown Copyright.](img/5uco_full.jpg)
![Image provided by GCHQ and reproduced here with kind permission from Director GCHQ [1]. Crown Copyright.](img/5uco_thumb.jpg "image # 5uco_full.jpg")
![Simplified mechanical operation. Based on [3].](svg/5uco_mech.svg)
![Simplified TX flow. Based on [3].](svg/5uco_tx.svg)
![Simplified RX flow. Based on [3].](svg/5uco_rx.svg)
![Converter from 7½ to 7 bits. Photograph via Jerry Proc [2].](img/7uco_converter.jpg)
![Fuses of the type that were used with the BID/30 (5-UCO). Photograph courtesy John Bowen [11].](img/fuses_large.jpg)
