Castle Bravo

Andrew Liang
March 18, 2017

Submitted as coursework for PH241, Stanford University, Winter 2017


Fig. 1: Castle Bravo Mushroom Cloud. (Source: Wikimedia Commons)

Operation Castle was an operation to test nuclear devices in the Marshall Islands during the spring of 1954. One of the more important nuclear operations during the Eisenhower administration, Castle proved not only how far nuclear weapons development had advanced but also furthered the arguments to ban testing due to radioactive fallout. On March 1 of that spring, the largest atomic bomb in United States history was detonated. Known as Castle Bravo, the device was detonated above Bikini Atoll generating a yield of 15 megatons or 1000 times the yield of the Hiroshima bombing. [1]


The first device tested of the Castle series, Bravo was lithium deuteride fueled with approximately 40% Li-6 and the rest Li-7. [1] Due to the assumption that Li-7 would be largely inert during the explosion, it was assumed that Bravo would generate a yield anywhere from 4 to 8 megatons. However, Li-7 underwent a reaction where a neutron that was bombarded at it would produce tritium, He-4, and an extra neutron, essentially turning it into an enriched Li-6 and causing the severe miscalculation in yield size. [2]

Upon detonation, an enormous 3-mile wide fireball composed of surrounding test equipment, coral, seawater and the bomb itself formed within seconds (Fig. 1). Within sixty-seconds the cloud rose to 45,000 feet and eventually reached an altitude of over 115,000 feet and 100 miles wide in diameter. [3] The crater left behind spanned 6,500 feet in diameter. [2]

Fig. 2: Castle Bravo Radiation Fallout. [5] (Source: Wikimedia Commons)

Radiation Effects

The detonation of Bravo also brought about accidental deposition of fallout on several nearby atolls, from Rongelap all the way to Utirik, and a Japanese fishing vessel (Fig. 2). This was due to unexpected eastward winds that pushed fallout outside the test area. Early radiation effects were observed in many of the inhabitants of Rongelap but it wasn't until a couple decades later when thyroid nodules and cancer developed in adults both at Rongelap and Utirik. In addition, there were two cases on growth retardation stemming from thyroid atrophy and numerous other cases of miscarriages and stillbirths. [4]

© Andrew Liang. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] D. M. Blades and J. M. Siracusa, A History of U.S. Nuclear Testing and Its Influence on Nuclear Thought, 1945-1963 (Rowman and Littlefield, 2014).

[2] J. Mahaffey, Atomic Accidents: A History of Nuclear Meltdowns and Disasters: From the Ozark Mountains to Fukishima (Pegasus Books, 2015)

[3] T. Kunkle and B. Ristvet, "Castle Bravo: Fifty Years of Legend and Lore," U.S. Defense Threat Reduction Agency, DIRTIAC SR-12-001, January 2013.

[4] J. Robbins and W. H. Adams, "Radiation Effects In The Marshall Islands," in Radiation and the Thyroid: Proceedings of the 27th Annual Meeting of the Japanese Nuclear Medicine Society, ed. by S. Nagataki (Excerpta Medica, 1989).

[5] S. Glasstone and P. U. Dolan, The Effects of Nuclear Weapons, 3rd Ed. (U.S. Government Printing Office, 1977), p. 437.