Operation WIGWAM was the U.S.
code name for an undersea nuclear test that took place in 1955, 500 miles southwest of
San Diego, CA. Designed to test the
vulnerability of submarines to
subsurface nuclear detonations (as from an
ASROC warhead) the test consisted of a 30-
kiloton atomic weapon which was suspended 2,000 feet below an unmanned (
duh!)
barge in 16,000 feet of water.
Several squaws (unmanned submarine-like hulls) containing recorders and other instrumentation were also moored beneath the surface, hung from the 6-mile long towline connecting the U.S. Navy tug and the barge holding the weapon. 30 ships were involved, including two that had been specially shielded against radiation - while 28 of the ships were 5 miles upwind of the shot, these two were 5 miles downwind with their crew buttoned up.
The Navy wanted to determine the characteristics of the shock wave produced when the entirety of the energy output of a nuclear weapon was contained underwater. They wanted to know how it propagated and how strong it would be. In addition, they wanted to measure the radioactive contamination from such a shot in order to figure out how these weapons could be utilized in combat.
No squaws survived the shot. Images of one of the squaws imploding from the inside can be seen in Trinity and Beyond: The Atomic Bomb Movie, which is highly recommended if you're interested in nuclear testing.