Operation Crossroads
1946 - Bikini Atoll lagoon, Marshall Islands, Pacific
The Crossroads Series tests were the first nuclear explosions since World War II, and the first nuclear weapon tests since Trinity. These were the first "weapons effects" tests ever conducted - tests designed specifically to study how nuclear explosions affect other things - rather than tests of the behavior of a weapon design (as was Trinity). The purpose of the tests was to examine the effects of nuclear explosions on naval vessels, planes, and animals.
A fleet of 71 surplus and captured ships anchored in the Bikini Atoll lagoon in the Marshall Islands were used as targets. This fleet included a number of famous Allied and Axis vessels such as the aircraft carrier USS Saratoga, the battleships USS Nevada, Pennsylvania, Arkansas, and New York; the German cruiser Prinz Eugen and Japanese battleshp Nagato.
Source: nuclearweaponarchive.org