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Definitions of “beam,” “draft,” “displacement”

1961: Thresher/Permit Class (U.S.)
Faster, Stronger, Deeper, Quieter


US Thresher/Permit Class
Thresher on April 30, 1961
Photograph courtesy U.S. Navy

The Thresher class of attack submarines was stronger, faster, deeper diving, and quieter than the Skipjacks, thanks to a variety of materials and streamlining improvements. The class’s name was changed to Permit after the submarine Thresher sank off New England in 1963, killing 129 (about the sinking).

The Thresher tragedy inspired creation of the SubSafe Program, attributed with dramatically improving safety for the entire U.S. submarine fleet.

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Length: 279 ft (85 m)

Beam: 32 ft (10 m)

Draft: 29 ft (9 m)

Displacement: 4,300 tons

Propulsion: 1 pressurized-water nuclear reactor, 1 propeller

Crew: 128

Armament: 4 21-inch (533-mm) torpedo tubes, mines

First Sub Commissioned: August 3, 1961

Maximum Speed: 30 knots (35 mph/56 kph)