Operation Sailor Hat was a series of explosives effects tests, conducted by the United States Navy Bureau of Ships under the sponsorship of the Defense Atomic Support Agency.

[5] The previous year in 1964, Operation Snowball was a 500-ton HE test on the Experimental Proving Ground in Alberta, Canada that provided technical information related to nuclear weapon detonation.

[1] Following the Japanese attack on Pearl Harbor, the Territory of Hawaii was placed under martial law and the island of Kahoʻolawe was used as a training ground, fleet bombing, and gunnery range.

[7] This made it a natural choice for Operation Sailor Hat, since it also had deep waters close to shore and was only 90 miles (140 km) away from the Pearl Harbor Naval Shipyard in Honolulu that could provide industrial support.

However, after undergoing extensive modifications at San Francisco Naval Shipyard she was converted to a target ship (reinstated as IX-304) to study the effects of high energy air explosions.

[8][1] Representative destroyer systems for communication, detection, fire control and weapons delivery were installed and an experimental reinforced fiberglass deckhouse was constructed for comparison with aluminum ones used at the time.

The TNT was supplied by the Naval Powder Factory in Hawthorne, NV that developed a method of producing high quality cast blocks from materials recovered from old torpedoes, mines and other weapons.

The Navy Construction Battalion Three had the hazardous task of carefully assembling 30,674 32.98-pound (14.96 kg) TNT blocks into 34-foot (10 m) hemispheres that reached a height of 17 feet (5.2 m) for each of the three tests.

[9] The crew reported the blast sounding like a large hammer hitting the ship that caused the deck to move out from under their feet and paint to flake off of piping and bulkheads.

[10] For the large surface shots, USS Atlanta was the primary close-in target ship, while the others were stationed more distantly so that they could be repaired more readily.

[1] A central timing and firing system was on board Atlanta to direct photo planes, smoke rockets and hundreds of recording instruments, the synchronization of which was essential.

The blast created an overpressure of 10 pounds per square inch (69 kPa) on the target,[11] a moving wall of highly compressed air with maximum wind speeds of 294 miles per hour (473 km/h).

An overpressure blast of that magnitude is equivalent to a 1 megatonne of TNT (4.2 PJ) burst at roughly 8,000 feet (2,400 m)[12] and is sufficient to be lethal and capable of destroying reinforced concrete buildings.