Brought to my project by alert reader Dennis Lindsay Lindsey Linse, who came across it in an article in the Washington Post magazine. An excerpt he sent:

The Code War
By Malcolm Tarlofsky
The Washington Post Magazine
10 May 1998

... With less than a year's experience in cryptanalysis, Phillips was sent to help out on another low-priority project, vaguely referred to as "the Russian problem."

There he would discover a numerical quirk that would lead, through many twists and turns, to the exposure of a vast network of Soviet spies and change the course of the Cold War.

The Russian problem would acquire the code name Venona, and it would engage an army of cryptanalysts in sifting through 1 million Soviet telegrams that had been encrypted in a theoretically unbreakable code. In time the SSA [Signals Security Agency] would be supplanted by the National Security Agency, and computers would take over the making and breaking of codes, but work on Venona would continue for 37 years, and it would be done by men and women using pencil and paper. To retrace their steps is to walk through one of the most daunting puzzles of the century and see it solved, bit by bit.