H-Bomb Effects: “Operation Castle Military Effects Studies” 1954 AF Special Weapons Project


H-Bomb Effects: “Operation Castle Military Effects Studies” 1954 AF Special Weapons Project
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Armed Forces Special Weapons Project military effects studies of the Operation Castle 1954 thermonuclear weapons tests (hydrogen bomb tests) are summarized, including Castle Bravo, 15 megatons, the largest atmospheric explosion ever conducted by the United States.

Reupload of a previously uploaded film, in one piece instead of multiple parts, and with improved video & sound.

Public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).


Operation Castle was a United States series of high-energy (high-yield) nuclear tests by Joint Task Force SEVEN (JTF-7) at Bikini Atoll beginning in March 1954. It followed Operation Upshot-Knothole and preceded Operation Teapot.

Conducted as a joint venture between the Atomic Energy Commission (AEC) and the Department of Defense (DoD), the ultimate objective of the operation was to test designs for an aircraft-deliverable thermonuclear weapon.

Operation Castle was considered by government officials to be a success as it proved the feasibility of deployable “dry fuel” designs for thermonuclear weapons. There were technical difficulties with some of the tests: one device had a yield much lower than its predicted yield (a “fizzle”), while two other devices detonated with over twice their predicted yields. One test in particular, Castle Bravo, resulted in extensive radiological contamination of nearby islands (including inhabitants and U.S. soldiers stationed there), as well as a nearby Japanese fishing boat (Daigo Fukuryū Maru), resulting in one direct fatality and continued health problems for many of those exposed. Public reaction to the tests and an awareness of the long-range effects of nuclear fallout has been attributed as being part of the motivation for the Partial Test Ban Treaty of 1963…

Operation Castle was intended to test lithium deuteride (LiD) as a thermonuclear fusion fuel. A solid at room temperature, “dry” LiD, if it worked, would be far more practical than the cryogenic liquid deuterium fuel in the Ivy Mike device. The same Teller-Ulam principle would be used as in the Ivy Mike “Sausage” device, but the fusion reactions were different. Mike fused deuterium with deuterium, but the LiD devices would fuse deuterium with tritium. The tritium was produced during the explosion by irradiating the lithium with fast neutrons…

The most notable event of Operation Castle was the ‘Castle Bravo’ test. The dry fuel for ‘Bravo’ was 40% Li-6 and 60% Li-7. Only the Li-6 was expected to breed tritium for the deuterium-tritium fusion reaction; the Li-7 was expected to be inert…

Consequently, the Li-7 component turned out to be an excellent source of tritium through a previously unquantified reaction. In actuality, ‘Bravo’ exceeded expectations by 250%, yielding 15 Mt — 1,000 times more powerful than the Little Boy weapon used on Hiroshima. Castle ‘Bravo’ remains to this day the largest atmospheric detonation ever conducted by the United States, and the seventh largest ever detonated in the world.

Because Castle ‘Bravo’ greatly exceeded its expected yield, JTF-7 was caught unprepared. Much of the permanent infrastructure on Bikini Atoll was heavily damaged. The intense thermal flash ignited a fire at a distance of 20 nautical miles (37 km) on the island of Eneu (base island of Bikini Atoll). The ensuing fallout contaminated all of the atoll, so much so, that it could not be approached by JTF-7 for 24 hours after the test, and even then exposure times were limited.

As the fallout spread downwind to the east, more atolls were contaminated by radioactive calcium ash from the incinerated underwater coral banks. Although the atolls were evacuated soon after the test, 239 Marshallese on the Utirik, Rongelap, and Ailinginae Atolls were subjected to significant levels of radiation… though the short-term effects of the radiation exposure for most of the Marshallese were mild and/or hard to correlate, the long-term effects were pronounced. Additionally, 23 Japanese fishermen aboard Lucky Dragon No. 5 were also exposed to high levels of radiation. They suffered symptoms of radiation poisoning, and one crew member died in September 1954.