Operation Sandstone - Operations

Operations

As in Operation Crossroads, each detonation was given its own code name, based upon the Joint Army/Navy Phonetic Alphabet. All used modified Mark III assemblies, and were detonated from a 200-foot (61 m) towers. The timing of the detonations was a matter of compromise. The gamma ray measurement experiments required darkness, but the B-17 drones that would sample the clouds needed daylight to control them. As a compromise, the Sandstone detonations all took place shortly before dawn.

The X-Ray nuclear device used a levitated composite core. It was detonated on Enjebi just before sunrise at 06:17 on 15 April 1948, with a yield of 37 kilotons. The efficiency of utilization of the plutonium was about 35%; that of the uranium-235 was 25% or more. This was somewhat higher than Los Alamos' prediction. Observers watching from ships in the lagoon saw a brilliant flash and felt the radiant heat. A condensation cloud 5 nautical miles (9.3 km; 5.8 mi) in diameter of quickly enveloped the fireball, which glowed within the cloud. It took 45 to 50 seconds for the thunderous roar of the explosion to reach the observers.

About 20 minutes later, Bariko launched a helicopter to check on the cable winch was to collect samples. It also lowered boats to test radioactivity levels in the lagoon. B-17 pilotless drone aircraft were flown through the clouds, and a drone light tank was used to recover soil samples from the crater. Unfortunately, it became bogged and had to be towed out ten days later.

The Yoke nuclear device used a levitated all-uranium-235 core. It was detonated on Aomon just before sunrise on 1 May 1948 at 06:09, a day late due to unfavorable winds. The observers saw a similar flash and felt the same heat as the X-Ray blast, but the 6-nautical-mile (11 km; 6.9 mi) wide condensation cloud was larger, and the sound of the explosion more forceful. One observer likened it to the sound of "a paper bag which is forcefully burst in a small room". They were correct: its yield of 49 kilotons made it the largest nuclear detonation up to that time, but it was considered inefficient and wasteful of the fissile material.

Zebra, the third test, and the last of the Sandstone series, was detonated on Runit just before sunrise at 06:04 on 15 May 1948. This test was characterized by AEC Chairman David Lilienthal as the "hardest and most important" test of the three. By using one of the B class initiators, it demonstrated that these could still be used with confidence. The observers perceived the flash and blast as similar to the previous two tests, but this time the base of the condensation cloud was at 2,000 feet (610 m), which gave the observers an unobstructed view of the fireball, which therefore appeared to be brighter and last longer than the other two. Looks were deceiving: its levitated uranium-235 core produced a yield of 18 kilotons.

The procedures used in the previous tests were repeated, but this time the winch cable snagged, and the test samples had to be retrieved by a jeep, exposing its crew to more radiation. The Los Alamos personnel assigned to remove the filters from the B-17 drones had apparently carried out the procedure on X-Ray and Yoke without problems, but this time three of them suffered radiation burns on their hands serious enough to be hospitalized and need skin grafting. One of the men who had carried out the procedure for Yoke was then also found to have burns on his hands and was hospitalized too, but was discharged on 28 May. Once again the drone tank gave trouble, and bogged in the crater, but the soil samples were retrieved by the backup drone tank. Both tanks were subsequently dumped in the ocean.