On the coast of Kahoʻolawe, the smallest of the eight main volcanic islands of Hawaiian, is a large crater left behind by a violent test conducted by the US Navy in 1965. Back then, starting from the beginning of World War 2 until the 1990s, Kahoʻolawe was used as a training ground and bombing target by the US armed forces. Thousands of soldiers, sailors, and airmen trained on Kahoʻolawe for the brutal assaults on islands such as the Gilbert and Marshall Islands, and New Guinea in the Western Pacific. During the Korean War, the War in Vietnam and throughout the entire Cold War period, pilots practiced hitting mock-up airfields, military camps, radar installations, and missile sites on Kahoʻolawe.
In 1963, the three nuclear super powers of the world—the United States, the Soviet Union and the United Kingdom—signed the Limited Test Ban Treaty that banned all atmospheric tests of nuclear weapons. The ban was enforced to address the rising public anxiety over the magnitude of nuclear tests and the risk of nuclear fallout. The ban came at a time when the US Navy still had a thing or two to learn about nuclear bombs, especially how the Navy’s ships fared in the presence of a blast. Because they couldn’t detonate nuclear bombs above the ground, the Navy turned to regular explosives but in enormous quantities to simulate a nuclear bomb.
A series of three tests were conducted at Kahoʻolawe under Operation Sailor Hat. Several decommissioned ships were anchored offshore a few hundred meters from the coastline, and a large dome of TNT blocks—34 feet across and 17 feet high—containing 500 tons worth of explosives was detonated.
After the first test, the large crater the explosion gouged into the bedrock was filled with sand to minimize secondary damage caused by rock ejecta. Over this crater another of dome of TNT blocks were built for the second test. This was repeated for the third test.
500 tons of TNT awaiting detonation at Operation Sailor Hat.
Each of the three massive blasts could be seen for miles, by land, air and sea. Their shockwaves were so powerful that antennas, radars and other structures on the deck of the ships were ripped apart. A life size mannequin placed on the deck facing the blast was violently thrown over. Despite the topside damage, the 169-man navy crew and 60 scientific personnel who remained below deck experienced only a jolt equivalent to an Iowa-class battleship firing a nine gun 16-inch salvo. The Navy was impressed with how well the blast was resisted by their ships. Only some minor design improvements were needed to make the ships more robust.
Meanwhile on Kahoʻolawe, the crater left by the third blast remained unfilled and slowly as the ecosystem healed, a small anchialine or landlocked pond formed with an underground connection to the ocean. The “Sailor's Hat” crater is now home to two endemic species of shrimps.
For the last three decades, the state of Hawaii along with the US Navy has been engaged in a cleanup effort on the island trying to remove unexploded ordnances and revert the damages caused by nearly fifty years of munitions testing. Over $400 million have been poured into the effort, yet the job is far from over. A quarter of the island is still off-limits.