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. The tests consisted of two underwater explosions at San Clemente Island, California in 1964 and three surface explosions at Kahoolawe, Hawaii in 1965. They were non-nuclear tests employing large quantities of conventional explosives (TNT and HBX) to determine the effects of a nuclear weapon blast on naval vessels, and the first major test of this kind since Operation Crossroads in July 1946.
Each "Sailor Hat" test at Kahoolawe consisted of a dome-stacked charge of TNT high explosive detonated on the shore close to the ships under test. Since a TNT detonation releases energy more slowly than a nuclear explosion, the blast effect at close range was designed to be equivalent to a nuclear weapon at greater distance. The main ship used for testing was the former Cleveland-class light cruiser . In addition, the guided-missile frigates and , the guided-missile destroyers , , and , and the Royal Canadian Navy's escort destroyer all participated in the trial. These were a mixture of the obsolete, Atlanta being built during WWII, and the recently constructed Cochrane. The highly complex operation yielded data useful for determining and improving blast resistance of naval ships.
Background
When the Limited Test Ban Treaty came into effect in 1963, it prohibited nuclear testing in the atmosphere. The Defense Atomic Support Agency turned to alternative methods of generating airblast effects with high explosives. 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. In 1963, DASA called on the Bureau of Ships to conduct a full scale explosives test with conventional chemical explosives and a test site had to be chosen.
Following the Japanese attack on Pearl Harbor, the Territory of Hawaii was placed under martial law and the island of Kahoolawe was used as a training ground, fleet bombing, and gunnery range. This made it a natural choice for Operation Sailor Hat, since it also had deep waters close to shore and was only away from the Pearl Harbor Naval Shipyard in Honolulu that could provide industrial support.
Preparations
A test platform was needed for the operation that could mount a variety of equipment and structures. The light cruiser was decommissioned in 1949 and placed in the Pacific Reserve Fleet, then in 1962 earmarked for disposal. 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. The hull was cut down to the main deck level and two different types of destroyer deckhouses and three mast arrays were fitted. 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. It was noted that in such an unusual configuration the refitted Atlanta received many stares and comments while en route to the test site in Hawaii.
The preparation of the charges was in itself an engineering feat. 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. A total of 92,022 blocks were produced for the tests. The Navy Construction Battalion Three had the hazardous task of carefully assembling 30,674 TNT blocks into hemispheres that reached a height of for each of the three tests. The domes were placed on thin octagonal concrete pads close to shore. In order to obtain the desired results, the ships also needed to be moored at precise distances from the charge for each test. This proved a difficult task in high winds and was accomplished with help from the Bureau of Ships, the tug and salvage ships and