Just How Damaging Can an Intelligence Leak Be? Turns Out, Pretty Damaging

There has been a lot of talk about leaks in Congress and in the White house, so we were wondering just how damaging a leak can be. Both President Donald Trump and Congressional Democrats have accused each other of leaking classified information.

Turns out, loose lips really can sink ships, as one congressman proved in 1943.

In June 1943, the deficiencies of Japanese depth-charge tactics were stupidly revealed in a press conference held by U.S. Congressman Andrew J. May, a member of the House Military Affairs Committee, who had visited the Pacific theater and received many intelligence and operational briefings.

May mentioned the highly sensitive fact that American submarines had a high survivability rate because Japanese depth charges were fuzed to explode at too shallow a depth.

Various press associations reported the depth issue over their wires and many newspapers (including one in Honolulu, Hawaii) published it. Soon, Japanese forces were setting their depth charges to explode at a more effective average depth of 75 meters (250 ft), to the detriment of American submariners.

Vice Admiral Charles A. Lockwood, commander of the U.S. submarine fleet in the Pacific, later estimated that May's revelation cost the United States Navy as many as ten submarines and 800 seamen killed in action. The leak became known as The May Incident.

In the Pacific Theater of World War II, Japanese depth charge attacks initially proved fairly unsuccessful against U.S. and British submarines. Unless caught in shallow water, a submarine would just dive below the Japanese depth charge attack. The Japanese were unaware that the submarines could dive so deep. The old United States S-class submarines (1918–1925) had a test depth of 200 ft (61 m); the more modern fleet-boat Salmon-class submarines (1937) had a test depth of 250 ft (76 m); the Gato-class submarines (1940) were 300 feet (91 m), and Balao-class submarines (1943) were 400 ft (120 m).

Depth charges, which had to be pre-set to the presumed depth of the enemy submarine, were replaced by the world's navies with anti-submarine missles around 1990. These are often heat seeking, and do not have to be pre-set.