25 July 1946
'Test Baker', Bikini Atoll

67 nuclear tests were conducted at Bikini Atoll. Map: Los Alamos National Laboratory

On 25 July 1946, the United States conducted the first-ever underwater nuclear explosion. Test Baker, detonated at the Bikini Atoll in the Pacific Ocean, was the fifth of over 2,000 nuclear explosions conducted to date. Of these, only a few were underwater explosions, carried out mainly to assess the damage to ships and submarines. The majority of the tests - around three quarters - were conducted underground and the rest in the atmosphere, apart from a handful of nuclear tests in outer space, such as the 1962 Starfish Prime test.

Admiral Blandy, Mrs Blandy and Rear Admiral Lowry celebrating the end of Operation Crossroads

The Baker device was suspended under a ship around 30 metres below the sea surface and yielded 23 kilotons. The test followed the atmospheric Test Able on 1 July 1946, both using the same design as the Nagasaki bomb. The objective was the same: to assess the effects of a nuclear explosion on a fleet of ships and on animals. Both tests were part of the 'Operation Crossroads' that involved some 42,000 personnel, 242 ships, 156 airplanes and the relocation of all 162 residents from the Bikini Atoll.

Suffering as a whole among the animals was negligible.Official Report of Operation Crossroads
Decontamination efforts aboard the German cruiser Prinz Eugen

All of the pigs and most of the rats on the ships died either from the blast or from radiation exposure. Of the 57 target vessels, eight either sunk or capsized as a direct result of the explosion. Eight more suffered extensive damage. Most of the remaining ships were highly radioactive and remained so despite decontamination efforts, which consisted of scrubbing or spraying the decks. Their main result was to expose those involved to radioactivity, of which test Baker had produced considerably more than Able. Most of the surviving vessels had to be subsequently sunk as "too hot to handle".

The degree of radioactive poisoning of water and ships was impressive.Official Report of Operation Crossroads
Bikini Resurvey in 1947. Image Credit: National Museum of Natural History, Smithsonian Institution

In the year following the two tests, a group of scientists and technicians were sent to conduct a scientific resurvey in Bikini. They concluded that: “Clearly radioactivity had entered the food chain. Plankton glowed on photographic plates, as did the intestinal tracts of the fish that fed on them. Only long term studies would show if the atoll would ever return to the ecological balance it enjoyed before Able Day.”

Half a century later in 1997, the International Atomic Energy Agency reported that the Bikini Atoll was still uninhabitable. Read more on the health and environmental impacts of the United States’ nuclear testing programme and the Marshallese claims for compensation.

 

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Next featured nuclear test:

6 and 9 August - Hiroshima and Nagasaki