[3]: p.33ff [4] The KL-7 had rotors to encrypt the text, most of which moved in a complex pattern, controlled by notched rings.

In 1953, AFSA's successor, the U.S. National Security Agency, introduced the machine in the US Army and Air Force, the FBI and CIA.

It was about the size of a Teletype machine and had a similar three-row keyboard, with shift keys for letters and figures.

There was an adaptor available, the HL-1/X22, that allowed 5-level Baudot punched paper tape from Teletype equipment to be read for decryption.

To establish a new encryption setting, operators would select a rotor and place it in a plastic outer ring at a certain offset.

A signal, coming from a letter key, went through the rotors, back to the permutor board to continue to the printer.

Therefore, depending on the Encipher or Decipher position of the permutor board, the direction of the signal through the rotors was changed.

The combination of cam rings and the controlling of a rotor by several switches created a most complex and irregular stepping.

In 1967, when the U.S. Navy sailor John Anthony Walker walked into the embassy of the Soviet Union in Washington, DC seeking employment as a spy, he carried with him a copy of a key list for the KL-47.

Proc (2005) differs, saying that, "after the Walker family spy ring was exposed in the mid-1980s (1985)...immediately, all KL-7's were withdrawn from service"[6]