In the wake of World War II, in a move closely related to the beginnings of the Cold War, the United States of America decided to resume nuclear testing in the Pacific Ocean, on Bikini Atoll in the Marshall archipelago.

Nevada, the target vessel for Able

Marshall Islands is composed of 29 atolls and five islands scatter over 357,000 square miles. This lonely part of the world is located north of the equator in the Pacific Ocean. This area is known as Micronesia. Bikini Atoll is one of these atolls. It is formed of 23 islands, totaling 3.4 square miles (8.8 km2) surrounding a deep 229.4 square mile (594.1 km2) central lagoon.

Navy tug sprays down USS New York after Baker

In February of 1946 Commodore Ben H. Wyatt, the military governor of the Marshalls, traveled to Bikini and invited the Bikinians to leave their atoll temporarily so that the United States could begin testing atomic bombs for "the good of mankind and to end all world wars."

Pennsylvania is scuttled off Kwajalein

Preparations for the U.S. nuclear testing program advanced rapidly. This plan was codenamed Operation Crossroads. It was a series of two nuclear weapon tests in July 1946. The purpose of the tests was to investigate the effect of airborne and underwater nuclear explosions on warships, equipment, and material and to stage an impressive display of American nuclear power. It was a vast military-scientific experiment.

Prinz Eugen moored in Bikini Atoll during Operation Crossroads

These tests were witnessed by hundreds of reporters, politicians, and international observers, along with 42,000 military and scientific personnel.

Decontamination efforts aboard Prinz Eugen

A fleet of 95 target ships was assembled in Bikini Lagoon. The target 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.

Tittle.- Operation Crossroads - Able And Baker Day Tests (1946): Documents Able Day and Baker Day blasts of the atomic bomb tests at Bikini Island in the Pacific. Contains footage from many of the ground and aerial cameras set up to record the blasts, beginning with B-29 aircraft "Dave's Dream" dropping an atomic bomb on Bikini Atoll

All of them were hit with detonations of two bombs identical in design and yield to the bomb used on Nagasaki:

• The first test was Able, an air strike. The bomb was dropped from the B-29 Superfortress Daves Dream on July 1, 1946 and detonated 520 feet (158 m) above the target fleet. It caused less than the expected amount of ship damage. Five ships were sunk.

Tittle: Operation Crossroads: Atomic Tests (1946) - Atomic bomb testing at Bikini Atoll is the subject of this 1946 Navy documentary. Part 1 covers the Able Test detonated on 1 July 1946. 

Tittle: Operation Crossroads: Atomic Tests (1946) -  Atomic bomb testing at Bikini Atoll is the subject of this 1946 Navy documentary. Part 2 includes footage of the aftermath of the Able test, and preparations for the Baker test.

• The second test was Baker, a underwater strike. The bomb was detonated 90 feet (27 m) underwater on July 25, 1946, sending up a spectacularly massive spray of steam and wáter. The Baker test's radioactive contamination of all the target ships was the first case of immediate, concentrated radioactive fallout from a nuclear explosion.

Tittle: Operation Crossroads: Atomic Tests (1946) -  Atomic bomb testing at Bikini Atoll is the subject of this 1946 Navy documentary. Part 3 shows the underwater Baker test on 25 July 1946, and the resulting damage to the target fleet.

Tittle.- Operation Crossroads (Baker Event 1946)

The Crossroads tests were the first of many nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand and observed by an invited audience, including a large press corps.

Tittle: Two Nuclear test: Able and Bake

The two atomic bomb blasts of Operation Crossroads were both about the size of the nuclear bomb dropped on Nagasaki, Japan. Eighteen tons of cinematography equipment and more than half of the world's supply of motion picture film were on hand to record the Able and Baker detonations.

Between 1946 and 1958, a number of 23 nuclear devices were detonated by the United States at seven test sites located on the reef, inside the atoll, in the air, or underwater. The cumulative force of the tests in all of the Marshall Islands was equivalent to 7,000 times that of the Hiroshima bomb.

Tittle.- Project Crossroads - Nuclear Test Film (1946): Project Crossroads was a series of two nuclear tests, Able and Baker, the first tests conducted at the Pacific Proving Ground, near the Bikini Atoll in the Marshall Islands. These were the fourth and fifth nuclear detonations in history, following the Trinity test in July 1945 and the two weapons dropped on Japan to end World War II. 
The two bombs used in Crossroads were of the Fat Man configuration, very similar to the implosion-type weapons tested at Trinity and dropped on Nagasaki, Japan. It had a plutonium pit. The only other nuclear weapon available at the time was the uranium gun-type Little Boy, which was dropped on Hiroshima, Japan. The Fat Man was a more complex weapon than Little Boy, thus needing more testing to gain experimental data. On July 24, 1946, the Baker shot was set off in the Bikini lagoon at a depth of about 90 feet with a yield of 21 kilotons. Two million tons of water were contained in the eruption and two million yards of sediment were removed from the lagoon floor. Nine ships were sunk.

Three Views of USS Saratoga Poster as the aircraft carrier rests on Bikini's lagoon. While some of the small print may not be readable, it gives one an idea of what to expect when diving on the ship.

USS Independence showing blast damage from Able, before Baker made her radioactive.