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US rotor-based cipher machine - this page is a stub

The KL-47 was an electro-mechanical rotor-based off-line cipher machine, 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 unit (right).

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 remains static.

The KL-47 was used for many years by the US Navy Command Center for Atlantic Submarine Forces [2] and was badly compromised. 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 radio channels. The last KL-47 in use was a naval version, which was decommissioned in 1984 [1].

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 [8].

  • KLB-47
    This is the base unit that contains the motor, the gear box, the generator and the elctronic circuits.

  • KLK-47
    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.

  • KLA-47
    The complex stepping unit, that senses the notches of the 7 movable rotors and controls the stepping motion of the other rotors.
  • HL-1
    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 [7].

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:

AN/SGA-3 code group block diagram [7]

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 [7].

AN/SGA-5 code group block diagram [7]

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 [2], it can be assumed that the Russians were able to read (break) messages encrypted with a number of high-level US cipher machines, including the KW-7, the KL-7 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 [5].

Walker joined the US Navy in 1955 and started spying for the Soviets in December 1967, when he had financial difficulties [3]. 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.
Photograph showing John Anthony Walker during his trial. Taken from

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.

Rotor reader
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 [2]. This allowed the Russians to decrypt at least one million sensitive classified (TOP SECRET) messages [4].

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 [6].

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) [6].

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.

3D view of the rotor reader. Copyright Paul Reuvers 2011.

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 [2].

Help required
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.

  1. Jerry Proc, KL-47
    Website, last updated 30 Oct 2012. Retrieved October 2013.

  2. 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.

  3. Wikipedia, John Anthony Walker
    Retrieved November 2010.

  4. FBI, The Year of the Spy
    Famous Cases and Criminals. John Anthony Walter Jr.
    Retrieved November 2010.

  5. Pete Earley, Family of Spies: The John Walker Jr. Spy Case
    TruTV website, crime library. Date unknown.

  6. H. Keith Melton, The Ultimate Spy Book
    ISBN: 07894074435. 2009.

  7. HL-1 CSP-6620A, TSEC/HL-1 and TSEC/HL-1B system block diagrams
    4 June 1962. Unclassified.

  8. UK/US Communications Security Conference 1951
    London, July 1951. US Army, 17 August 1951.
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