Operation Ivy

Operation Ivy was a pair of U.S. nuclear weapon tests in the Marshall Islands in 1952, which both provided experimental verification, with a prototype (Ivy Mike), of the Teller-Ulam design for fusion weapons, and also of a backup using an exceptionally high-yield fission device (Ivy King).

Ivy Mike
Ivy Mike was a ground test of a prototype called the Sausage, far too large to airdrop but using the Teller-Ulam principle of staged radiation implosion. Teller himself did not participate, but the development effort, coded Project Panda, was conducted by the Panda Committee at Los Alamos, under J. Carson Mark.

The device was build around a Mark 5 primary, "and a secondary stage consisting of liquid deuterium fusion fuel stored in a cylindrical Dewar (thermos) flask. Running down the center of the Dewar was a plutonium "spark plug" rod to ignite the fusion reaction. The Dewar was surrounded by a natural uranium pusher/tamper weighing more than 5 metric tons. The entire assembly was housed in an enormous steel casing, 80 inches wide and 244 inches long, with walls ~10-12 inches thick, the largest single forging made up to that time. The inside surface of the casing was lined with sheets of lead and polyethylene to form the radiation channel that conducted heat from the primary to the secondary. The entire device weighed 82 tons."

It produced the fourth largest yield of any U.S. test. "77% (8 megatons) of the yield was due to fast fission of the natural uranium pusher/tamper, with remainder (2.4 megatons) coming directly from fusion of the deuterium fuel. The island the test device was installed on, Elugelab (code named Flora), was entirely destroyed. The resulting crater was 6240 ft across and 164 ft deep." "High levels of radiation blanketed much of the atoll following the test. The mushroom cloud climbed to 57,000 feet in only 90 seconds, entering the stratosphere. One minute later it reached 108,000 feet, eventually stabilizing at a ceiling of 120,000 feet. Half an hour after the test the mushroom stretched 60 miles across, with the base of the mushroom head joining the stem at 45,000 feet."

Ivy King
Ivy King was a prototype of the Mark 18 (nuclear weapon), also called the "Super Oralloy Bomb (SOB)", which would be obsolete if the Ivy Mike prototype could be turned into an air-droppable bomb. Still, Ivy King was airdropped from a B-36 bomber, detonating at 1480 feet and yielding 500 kilotons. It was designed by Ted Taylor at Los Alamos, and remains the most efficient pure fission bomb ever tested.

The Ivy King device was based on the operational Mk-6D bomb, but used the 92 point implosion system designed for the Mark 13 (nuclear weapon), and a unique fission pit containing an unusually high amount of oralloy, or highly enriched uranium. Pits of operational bombs mixed uranium and plutonium.

The 60 KG of oralloy made up several critical masses and used improvised safety mechanisms to prevent a criticality accident in the event of a crash.

It was confirmed obsolete by the Operation Castle test two years later, in which a weaponized thermonuclear bomb was airdropped.