Bikini Atoll Nuclear Test: Underwater detonation of 23 kiloton nuclear weapon, 1946

 

The explosion, known as the Baker Test, was part of Operation Crossroads at Bikini Atoll in the Pacific. The purpose of the tests was to investigate the effect of nuclear weapons on warships. The Crossroads test was the first of several nuclear tests conducted in the Marshall Islands and was publicly announced in advance and witnessed by an invited audience including a large press corps.

A fleet of 95 target ships was assembled in Bikini Lagoon. In the center of the target group, the density was 20 ships per square mile (7.7 per square km), three to five times higher than military doctrine allowed.

The stated goal was not to simulate a realistic anchorage, but to measure damage at as many different distances as possible depending on distance from the explosion center.

This arrangement also reflects the outcome of an Army/Navy disagreement over how many ships should be allowed to be sunk. The target fleet included four obsolete American battleships, two aircraft carriers, two cruisers, eleven destroyers, eight submarines, several auxiliary and amphibious ships, and three surrendered German and Japanese ships.

The ships carried sample quantities of fuel and ammunition as well as scientific instruments to measure air pressure, ship speed, and radiation. Live animals on some of the targeted ships were supplied by the support ship USS Burleson, which brought 200 pigs, 60 guinea pigs, 204 goats, 5,000 rats, 200 rats, and worm-infested grains for study of the genetic effects by the National Cancer Institute. Institute. Amphibious target ships were stationed at Bikini Island.

At Baker on 25 July, the weapon was slung beneath a landing craft LSM-60 anchored in the middle of the target fleet. Baker was detonated 90 feet (27 m) underwater, halfway down in water 180 feet (55 m) deep, with an intensity of 23 kilotons. No identifiable parts of the LSM-60 were ever found; It was probably vaporized by the nuclear fireball.

The Baker shot produced so many unusual events that a conference was held two months later to standardize nomenclature and define new terms for use in description and analysis. The underwater fireball took the form of a rapidly expanding bubble of hot gas that pushed against the water, generating a supersonic hydraulic shock wave that crushed the hulls of nearby ships as it spread.

When the diameter of the gas bubble equaled the depth of the water, 180 feet (55 m), it hit the sea floor and the ocean surface simultaneously. At the bottom, it began digging a shallow crater, which was eventually 30 feet (9 m) deep and 2,000 feet (610 m) wide.

At the top, it pushed the water above it into a "spray dome", which erupted from the surface like a geyser. The time elapsed after the explosion was four milliseconds.

As the bubble reached the air, it triggered a supersonic atmospheric shock wave that, like the crack, was more dramatic than destructive. The brief low pressure behind the shock wave immediately produced fog that enveloped the developing column in a "Wilson cloud", also known as a "condensation cloud", obscuring it from view for two seconds.

The Wilson cloud began in the hemisphere, expanded into a disk that rose above the water and revealed a full-blown spray column, then expanded into a donut and disappeared.

Following the Baker decontamination problems, the United States Navy equipped newly built ships with countermeasure washdown systems (CMWDS) of piping and nozzles so that when a nuclear attack appeared imminent the ship's exterior could be sprayed with salt water spray from the fire suppression system. Surfaces to be covered. The film of flowing water will theoretically prevent contaminants from settling in cracks and crevices.