American Cryptology during the Cold War - The Black Vault

After the war, the cryptologic community began the search for a reliable and efficient
on-line device. For a time it appeared that one-time tapes were the answer. The British
developed the 5UCO or the Secretape, which achieved limited use during the early 1950s.
But tape production and handling were still a nightmare, and the volume of
communications required in the 1950s dictated another solution.50
Circuit speeds were beginning to exceed the capability ofmechanical rotors to keep up.
What was needed was an electronic key generator. The solution was the NSA-developed
KW-26, the first on-line electronic key generator to come into wide use in the United
States. First fielded in 1957, the KW-26 remained the mainstay of U.S. enciphered text
communications for thirty years. According to a former NSA COMSEC official, the KW-26
made the Agency's COMSEC reputation. 61
The KW-26, because it was electronic rather than electromechanical, had no moving
parts, and its speed was limited only by the speed of the associated teletypewriters, which
at that time was up to 100 words per minute. Built during the transition from tubes to
transistors, the KW-26 had a little ofboth. It had a simple-to-set key system using cards
manufactured at NSA. When an operator pulled the card out ofthe machine, a knife sliced
it in half so that it could not be reused. Its chief disadvantage was that it could be used
only for point-to-point circuits, which dictated that a huge number of machines be
manufactured. At one time the NSA communications center alone had 336 ofthem.62
The point-to-point modus limited the KW-26's utility in the Navy. Naval
communications were marked by wide-area fleet broadcasts to large numbers of ships
afloat. Naval vessels needed the capability to tune into a broadcast at any time during the
day or night and just receive traffic - transmitting messages was a much smaller
communications function. To solve this problem, NSA designed the KW-37, a crypto
device that permitted a ship's communications operator to tune into the fleet broadcast
using a cryptographic catch-up function. 63 KW·37
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