keep individuals within the MPE. Times were calculated to keep the total exposure below two roentgens for the personnel working on the ships. A floating decontamination facility was created on board a transport ship for the Wahoo and Umbrella nuclear tests. This allowed important data analysis and an increase in recovery efficiency. Wahoo preparation The nuclear explosion was carried out in open ocean outside of Enewetak. This nuclear test codenamed Wahoo was the first underwater test in the Operation Hardtack series. This test could be considered a continuation of the Wigwam nuclear blast (a deep water nuclear test off the coast of San Diego). Like its predecessor, the Wahoo shot was a scientific program that studied the effects of an underwater nuclear blast on Navy systems. The nuclear device was positioned deep in the Pacific Ocean. This deep water test required precise targeting arrays to be set up around the blast location, which presented unique problems for the arrays as the winds, sea currents and tides needed to be within certain limits for the data to be accurate. Testing arrays were placed at depths of around the nuclear device. The deep water mooring systems needed for the test proved to be difficult to position, leading many analysts to believe the data skewed. The target ships to be used for this program consisted of three destroyers, an active submarine, a submarine mockup used in Wigwam tests, and a merchant marine ship. It was predicted that no air blast or thermal effects would be presented from the underwater blast. The fallout from the blast was also predicted to stay within the target array due to the southwest surface winds. Wahoo blast The test conditions were met on May 16 allowing for the nuclear device to be detonated. Within a second of detonation, a spray dome was created that reached a height of after seven seconds. The overall shape of the spray dome resembled a cone with 45 degree sloped sides. Plumes were seen breaking through the spray dome after six seconds in every direction. The vertical plume continued rising until 12 seconds after the blast while the lateral plumes traveled for 20 seconds before collapsing. The diameter of the spray dome was approximately at the 20 second mark. The base surge reached a radius of in the downwind direction after 1.7 seconds. The downwind surge aided by a wind reached speeds of