KW-26

It used vacuum tubes and magnetic core logic, replacing older systems, like SIGABA and the British 5-UCO, that used rotors and electromechanical relays.

A KW-26 system (transmitter or receiver) contained over 800 cores and approximately 50 vacuum-tube driver circuits, occupying slightly more than one half of a standard 19-inch rack.

The military services' requirements for numerous modes and speeds significantly increased costs and delayed delivery.

Card readers were cleaned and the spring loading of the contacts checked as part of the routine maintenance of the device.

The crystal controlled clock in the KW-26 was capable of keeping both ends of the circuit in sync for many hours, even when physical contact was lost between the sending and receiving units.

In practice, operational protocol led to the cards being replaced more often than was desirable to maintain maximum security of the circuit.

Other services demanded KW-26's and some 14000 units were eventually built, beginning in the early 1960s, for the U.S. Navy, Army, Air Force, Defense Communications Agency, State Department and the CIA.