Although Crossroads was a military program, the mobilization of scientific interests was in many ways of historic proportions. For months before the explosions, oceanographers studied the waters and the structure of the mid-Pacific basin and meteorologists the winds and upper airs. Geologists, zoologists, botanists, and other specialists examined the atoll in detail. Bikini became, as it remains to this day, one of the most thoroughly familiar ocean structures in the world. There was awareness, even then, of the significance of radioactivity as an element of nuclear effect. The task force made elaborate preparations to assure the safety of personnel and sent to the atoll thousands of radiation-detection instruments. Plans were made to observe the effects of radioactivity on test animals placed on ships of the target fleet. The Underwater Detonation The first of the Bikini events, Test Able, the explosion of a bomb dropped from an aircraft over the target fleet, sank a number of major vessels, left others sinking or crippled, contaminated many with radiation, and laid a plume of fallout northward over the rim of the atoll into the waters of the ocean. It was Test Baker, however, the underwater explosion, that would make Bikini the subject of radiobiological investigations for many years. The Baker test was the first occasion in which nuclear debris was mixed with water and ocean sludge and returned to the area of detonation. The explosive device was of what later would be called nominal size, its force equivalent to 20,000 tons of TNT. The test still is regarded as a classic demonstration of the phenomena of shallow-water atomic explosion. [Illustration: _The Baker Test. A cauliflower-shaped cloud, after dumping one million tons of water that had been sucked up by the explosion, rises over the target warships, silhouetted in front of the spreading base surge._] At the moment of release, the surface water of the lagoon was first lifted and then penetrated by a lighted bubble that vanished in seconds in a hollow column of water of gigantic dimensions—a column 2000 feet in diameter (its walls 300 feet thick) rising to a height of 6000 feet and containing 1,000,000 tons of water. At the base of the column, foam was churned upward for several hundred feet, and, moving out from the base, as the column sank back into the lagoon, surged a monstrous wave initially more than 80 feet high. Radioactivity in the water was intense. The immediate total was described as equal to “many hundred tons of radium”. Decay and dilution of radioactive materials quickly reduced the total radioactivity. After 3 days, by which time water contamination had spread over an area of 50 square miles, the dose rate from the water was well within safe limits for persons remaining for brief periods. Yet it was several more days before inspection and scientific parties could spend useful time among the surviving target vessels.