US rotor-based cipher machine
- this page is a stub
The KL-47 was an electro-mechanical rotor-based off-line
developed by the National Security Agency (NSA)
in the US
around 1960 and built by Teletype Corporation.
The machine is based on the principle of the
KL-7 and uses the same cipher wheels, but is slightly
larger, as it incorporates a paper tape reader/puncher and
a standard teletype keyboard.
The machine is also known as TSEC/KL-47, whilst the individual
components each have the TSEC-extension added as a suffix to their
name (e.g. KLB-47/TSEC). It consists of a rather high base unit
that contains the valve-based circuits and the keyboard.
On top of the base unit is a printer unit (left) and the rotor
The keyboard was similar to that of the Teletype Model 35 teleprinter
machine, making operation of the machine a bit smoother than the
KL-7. The machine is equipped with a paper tape printer and can be
extended with a tape reader (HL-1) and puncher (via HL-2 code converter).
The rotor unit on the right consisted of a basket with eight rotors,
and a complex stepping unit.
The machine was usually supplied with 12 differently wired cipher wheels,
of which 8 were placed inside the rotor basked, as per keylist or
operational procedure. Of the eight rotors, 7 are moved by the
complex stepping mechanism, whilst the remaining one in position 4
The KL-47 was used for many years by the US Navy Command Center for
Atlantic Submarine Forces  and was badly
On a number of (radio) networks it was also used as a backup in case
other means of communication had failed, for example due to bad HF
The last KL-47 in use was a naval version, which
was decommissioned in 1984 .
The KL-47 is backwards compatible with the KL-7, but not vice versa.
As KL-47 support a larger character set than KL-7, messages created on
a KL-7 can be decrypted on a KL-47, but when sending messages from
KL-47 to KL-7, the use of punctuation marks should be avoided .
This is the base unit that contains the motor, the gear box, the
generator and the elctronic circuits.
This is the rotor basket that contains a spindle with 8 cipher wheels
or rotors on it. Seven of these rotors can be stepped, whilst the remaining
one (in position 4) remains static. The basket can be removed from the
machine by releasing two levers; one at either side of the basket.
The complex stepping unit, that senses the notches of the 7 movable
rotors and controls the stepping motion of the other rotors.
An external HL-1 paper tape reader was available for reading 5-level
teleprinter data straight into the KL-47, which could then be
enciphered or deciphered by the KL-47.
On its own, the KL-47 accepts input from its built-in keyboard only.
In order to read the ciphertex directly from a 5-level paper tape,
the optional 50 WPM (HL-1) tape reader could be installed, which converts
the teletype signal into the format used for the KL-47 .
By default, the output is presented as printed text on a 9.5 mm (3/8")
paper strip, but special arrangements were possible to allow the output
to be converted directly to 5-level paper tape, for example in the AN/SGA-3
code group, that consists of a KL-47 with HL-1B, HL-2 and a puncher:
In this case the HL-1B and HL-2 are both suitable for a speed of 65 WPM.
Furthermore both devices and insert and ignore formatting spacing when
appropriate, depending on whether the input comes from a ciphertext
or plaintext paper tape. In this case, the output is punched on
a standard Model 14 typing reperforator and/or printed on a Model 28
pape printer .
An even more complex arrangment is shown in the block diagram of the
AN/SGA-5 code group above. In this case the ciphertext is received by
radio in morse code, after which it is printed and punched by a
combination of a Model 28 page printer and a Model 14 tape puncher.
The ciphertext paper tape is then fed into the KL-47 via a HLT-1
tape reader and a HLI-1 translator.
During its lifetime, KL-47 was compromised several times.
Based on publicly available research ,
it can be assumed that the Russians were able to read (break) messages
encrypted with a number of high-level US cipher machines, including
and the KL-47.
The most famous story of cipher compromise is that of John Anthony
Walker, born 1937, who worked for the US Navy and successfully spied for the
Russians for nearly 17 years .
Walker joined the US Navy in 1955 and started spying for the Soviets in
December 1967, when he had financial difficulties .
From that moment, until his retirement from the navy in 1983,
he supplied the Russians with the key lists and other critical cipher
material of the KL-47, the KW-7 and other cipher machines.
For his information he received several thousand dollars from the Soviets
each month. In 1969 he began searching for assistance and befriended
Jerry Whitworth, a student who would become a Navy Senior Petty Officer.
In 1973, he was able to enlist Whitworth in his spy-ring.
In 1976, Walker left the Navy to become a Private Investigator (PI), but kept
spying for the Russians. By 1984, he had recruted his older brother Arthur
and his son Michael, who kept the endless flow of classified documents going.
He also tried to recruit his youngest daughter who had started to work
for the US Army, but this attempt failed when she became pregnant and
abandoned her military career.
Earlier, around 1976, Walker and his wife Barbara divorced.
When he refused to pay alimony in 1985, Barbara tipped-off the FBI,
which eventually led to Walker's arrest.
After his arrest, Walker cooperated with the authorities
and pleaded guilty, in order to lower the sentence of his son Michael.
The information passed by John Walker and his spy ring,
allowed the Russians to build an analog of the KL-47
and to find ways to mount a cryptanalytical attack on the machine .
This allowed the Russians to decrypt at least one million sensitive
classified (TOP SECRET) messages .
The Russians even supplied him with a small device, called a rotor reader,
that allowed him to easily trace the internal wiring of each rotor .
The image on the right shows the device, as it was confiscated by the FBI.
It was small enough to be carried inconspiciously, and could easily be
hidden in a pocket. When folded it measures approx. 7.5 x 10 cm
(about a pack of cigarettes).
The device consists of two halves that are kept together by springs and
hinges. Once opened, 36 flat-faced contacts become visible. They
mate with the 36 spring-loaded contacts of a KL-7 rotor
(photograph supplied by Keith Melton) .
A hand-operated slide contact, hidden inside a storage compartment at the
top left, was then inserted through the center hole of the rotor.
It kept the rotor in place, provided the correct pressure for the spring-loaded
contacts, and allowed the slide contact to 'brush' over each individual rotor
contact at the other side. The rotor would be placed with index arrow
opposite the position 0 index of the reader. The slide contact was then moved
over the individual contacts of the rotor, and each time one of 36 lamps on the
lamp panel (at the left) would be lit.
Below is a 3-D drawing of the rotor reader. It gives a good idea of
how it was used. The manually operated slide contact is here taken out
of its storage compartment. It has a rectangular 'key' at the bottom
(left in the drawing) that is inserted in the rectangluar hole
at the center of the reader.
It is assumed that the rotor reader was not one-of-a-kind,
but that at least a modest quantity of them was built.
The Soviets supplied Walker with the device only three weeks after he
started spying for them in 1967. Furthermore, Walker was not the only
person who compromised the KL-47 and similar machines.
When Army Sergeant Joseph Helmich was caught spying in the mid-1970s,
an identical rotor reader was found on him .
For a detailed description of the rotors, the stepping mechanism
and the gearbox, please refer to our KL-7 page.
The KL-47 works much in the same way.
We currently have no other information about the KL-47. You can help us
expanding this page by supplying additional details and stories.
If you think you can help, please contact us.
- Jerry Proc, KL-47
Website, last updated 30 Oct 2012. Retrieved October 2013.
- Laura H. Heath, Analysis of Systematic Security Weaknesses of the US Navy...
M.S., Georgia Institute of Technology, 2001.
Fort Leavensworth, Kansas (USA), 2005.
Thesis of Major Laura Heath, detailing how John Walker exploited weaknesses
in the US Navy Broadcasting System between 1967 and 1974.
- Wikipedia, John Anthony Walker
Retrieved November 2010.
- FBI, The Year of the Spy
Famous Cases and Criminals. John Anthony Walter Jr.
Retrieved November 2010.
- Pete Earley, Family of Spies: The John Walker Jr. Spy Case
TruTV website, crime library. Date unknown.
- H. Keith Melton, The Ultimate Spy Book
ISBN: 07894074435. 2009.
- HL-1 CSP-6620A, TSEC/HL-1 and TSEC/HL-1B system block diagrams
4 June 1962. Unclassified.
- UK/US Communications Security Conference 1951
London, July 1951. US Army, 17 August 1951.
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