Operation Sailor Hat was an underwater and surface high-explosive test program conducted in 1965 by the U.S. Navy Bureau of Ships (BuShips) under the sponsorship of the Defense Atomic Support Agency (DASA). This program consisted of two series of underwater explosions, three surface explosions at San Clemente Island, California, and three surface explosions at Kaho`olawe Island, respectively. The three 500-ton Trinitrotoluene (TNT) charges were constructed on the beach above the water line on the southwest coast of Kaho`olawe.
In May of 1941, Kaho`olawe Ranch signed a sublease for a portion of the island with the U.S. Navy for $1.00 a year up to 1952 when the Ranch's lease expired. Seven months later, on the day following the Japanese attack on Pearl Harbor (December 8, 1941), the Territory of Hawaii was placed under martial law. The military took over the entire island, and ranching operations ended. Ship-to-shore bombardment of the island commenced in 1941 and intensified starting on October 21, 1943, when the USS Pennsylvanin conducted rehearsals for the Gilbert Islands invasion. In preparation for additional landings across the Pacific, the Navy ran ship-to-shore fire control training operations at Kaho`olawe. During the Korean War era, weapons usage shifted from naval projectiles to air-dropped, general purpose bombs. Targets and mock airfields were built on-island for practice air attacks and strafing runs.
Bitter wartime experience taught the Navy the need to subject ships, aircraft, weapons and equipment to conditions simulating the destructive forces of combat. Explosive tests to determine the survivability of warship structure and installations are frequently conducted, usually on obsolete ships that are not necessarily expected to survive the experience, but sometimes using modern units which have many years of active service ahead of them.
Among the most spectacular of these tests were three very powerful conventional explosions carried out at Kahoolawe Island, Hawaii, in 1965 as part of Project "Sailor Hat", intended to study the effects of shock and blast on warships built to contemporary design standards. Other modern ships were also assigned as targets, though they would be stationed more distantly from the explosions to ensure that any resulting damage could be readily repaired. Each of the "Sailor Hat" tests used a 500-ton charge of high explosive, stacked in hemispheric form on Kahoolawe's rocky shore.
The former light cruiser Atlanta (IX-304) was specially converted as a close-in target ship for this operation. Atlanta (IX-304), off the San Francisco Naval Shipyard, configured for Operation "Sailor Hat," presented an interesting silhouette to those familiar with her original rig as a Cleveland-class, light cruiser. Various experimental ship superstructures for new generations of guided missile frigates and guided missile destroyers were evaluated. The tests were conducted to determine whether the experimental structures could satisfactorily combine essential lightness with strength and blast resistance. USS Atlanta IX-304, formerly the light cruiser CL-104, was modified with a prototype aluminum superstructure. Converted to a target ship, Atlanta was fitted with two different types of destroyer deckhouses and three mast arrays; representative destroyer communications, fire control, and weapons delivery systems were installed, while an experimental reinforced fiberglass deckhouse was constructed for comparison under air blast forces with aluminum deckhouses then in use on destroyers.
The 500-ton TNT explosive charge for Shot "Bravo", first of a series of three test explosions, was readied for detonation on the southwestern tip of Kahoolawe Island, Hawaii, in early February 1965. It was 17 feet high and 34 feet in diameter. In addition to Atlanta, the guided-missile destroyer Cochrane (DDG-21) and the Canadian Navy's escort destroyer Fraser were present for the first test, Shot "Bravo", which took place on 6 February 1965. All the ships had their crews on board for this spectacular blast, which resembled a small nuclear explosion in many ways. Afterwards the Pearl Harbor Naval Shipyard repaired the Atlanta and somewhat altered her radar antenna installations.
Prior to her first deployment, USS COCHRANE (DDG-21) was assigned to Operation "Sailor Hat." Operation sailor hat was a Navy project designed to test the survivability of the newer Navy ship designs to simulated nuclear blasts. Operation Sailor Hat simulated the blast effects of a nuclear explosion by detonating 500-tons of TNT in three separate tests on the Island of Kahoolawe, in the Hawaiian island chain. COCHRANE was present for the first test shot "Bravo" on 6 February 1965 along with the Canadian Destroyer Escort FRASER and the US Navy test ship ATLANTA (IX-304), (ex-CL-104). After the test shot COCHRANE lost power for 5 minutes as the blast overpressure washed over her. Quickly restoring main power, she returned to the Pearl Harbor Naval Shipyard for a quick hull and systems inspection to gauge the effects of the blast. The yard was impressed with how well the ship and crew rode out the blast. After some minor repairs (Both the 3-Dimensional AN/SPS-39 & 2-Dimensional AN/SPS-40 Air Search Radar Antennas had to be replaced) and routine maintenance COCHRANE was cleared for her first deployment.
The 500-ton TNT explosive charge for Shot "Charlie", second of a series of three test explosions, was ready for detonation on the southwestern tip of Kahoolawe Island, Hawaii, in April 1965. On 16 April the second test, Shot "Charlie", was conducted with Atlanta, guided-missile frigate England (DLG-22), guided-missile destroyer Benjamin Stoddert (DDG-22) and HMCS Fraser nearby.
The series concluded with Shot "Delta" on 19 June 1965. In addition to Atlanta, the guided missile frigate Dale (DLG-19) and guided missile destroyer Towers (DDG-9) were present on that occasion. Operation Sailor Hat involved using numerous conventional explosives to simulate nuclear blasts. Delta, the last Sailor Hat test in the ship evaluation program, was conducted to study seismological data, underwater acoustics, radio communications, cratering, air blast effects, cloud growth, fire ball generation, and electromagnetic data.
The crater resulting from the first detonation was subsequently back filled and is no longer visible. The second and third detonations were conducted at the same site; the result is the present "Sailor's Hat" crater. Sailor's Hat crater has formed an aquatic ecosystem which has become habitat for two endemic species of shrimp: Halocaridina rubra and Metabataeus lohena.
In 1993, Senator Daniel K. Inouye of Hawaii sponsored Title X of the Fiscal Year 1994 Department of Defense Appropriation Act (PL 103-139, 107 Stat. 1418. 1479-1484). Title X authorized conveyance of Kaho`olawe and its surrounding waters to the State of Hawaii. It also provided for the "clearance or removal of unexploded ordnance" and environmental restoration of the island, to provide "meaningful safe use of the island for appropriate cultural, historical, archaeological, and educational purposes, as determined by the State of Hawaii."
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