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Fissionable Material and Processes



Port Chicago Naval Magazine:

Contra Costa County, California. Constructed 30 miles NE of San Francisco, California, on Suisun Bay; authorized December 9, 1941 by Secretary of the Navy Frank Knox. Ammunition loading aboard civilian deep water transports destined for the Pacific Theater of war commenced November 1942.

The Navy facility was identified by the nearest United States post office and thus designated Port Chicago by reference to the small rural town that lay one and one-half miles inland from the southern shore of Suisun Bay at the base of a range of low hills south of the town. Beyond the hills lay a fertile expanse of small and picturesquely lovely small California farms and orchards that since World War II have been entirely transformed to accommodate the present population of one million, of whom 120,000 live in the city of Concord.

The Port Chicago magazine was served by the Santa Fe, Southern Pacific and Western Pacific rail roads by which the flow of wartime munitions to the magazine could easily move from manufacturing plants across the country and, for example, from the remote and very much larger Navy munitions depot at Hawthorne, Nevada.

Ship loading operations at the facility pier were conducted by 1,000 African-American enlisted Navy personnel in 24-hour operations. The explosion of the fully laden Liberty ship E. A. Bryan at the magazine pier at 10:30 the evening of 17 July 1944 resulted in the immediate death of 320 men on and about the exploded ship and the injury of several hundred-sailors on the base and civilians in the surrounding territory. Destruction and damage at the base facilities was extensive, but the base was rapidly reconstructed and returned to service.

Fissionable and hardware components of the atomic bomb detonated in combat 6 August 1945 at Hiroshima, Japan, were transshipped through the Port Chicago base late in July 1945. The base has since continuously been a munitions transshipment facility operated by the Navy with contributions to the conduct of the Korean and Vietnamese wars and was the site of contentious antiwar protests and antinuclear demonstrations during the 1960s, 70s and 80s. The base since World War II has been the principal West coast transshipment, storage and repair facility for the Navy's nuclear weapons, but the site was recently transferred to the U.S. Army.

In consideration of the casualties of the 1944 explosion, the important role of the base during World War II and the national historical importance of the explosion, the Port Chicago Naval Magazine National Memorial was established by Congressional enactment (Public Law 102-562; 102d Congress) 28 October 1992 and signed into law by President George Bush. The National Memorial was dedicated by the National Park Service on the 50th anniversary of the explosion 17 July 1994.

Port Chicago Naval Mutiny:

In the aftermath of the explosion 300 uninjured African-American enlisted Navy men on the base en masse refused to comply when ordered to return to their assigned duty loading ammunition into the cargo holds of ships destined for the Pacific Theater of war. Although the Port Chicago Magazine shiploading pier had been destroyed in the explosion, the nearby Mare Island Naval Magazine piers were operational; to that facility the men were ordered to duty, which order they refused. Following confinement below decks on a barge at Mare Island the assembled men were addressed by the Commandant of the 12 Naval District (San Francisco) and instructed that they were subject to summary execution if they remained in defiance. Two hundred seventy-five men then agreed to return to duty as ordered and in summary courts-martial were convicted of insubordination and other offenses. Fifty of the men remained obdurate and were charged with mutiny-in-wartime and convicted of that charge by formal Navy court-martial. The Port Chicago mutiny is the largest mutiny in United States military history. Various legal reviews of the proceedings during 55 years sustained the convictions. On December 23, 1999, President William Clinton granted presidential pardon to one of the two known surviving Port Chicago mutineers, Mr. Freddie Meeks.


one of two or more atoms of an atomic element, the nuclei of which have the same number of protons but differ in the number of neutrons; the variation of neutron number among the nuclei of isotopes of the same element distinguish each isotope by a different atomic mass. In chemical reactions, all isotopes of the same element behave identically.


heavy silvery-white metallic element, radioactive, easily oxidized; atomic number 92, atomic weight 238.03, melting point 1,132?C, boiling point 3,818?C. Named in reference to the planet Uranus, and having 14 known isotopes of which U238 is the most abundant in nature. The peculiar nuclear properties of the U238 isotope determined that a fission chain reaction in U238 was, for practical purposes, unrealizable during World War II. In the isotope U235, however, conditions are favorable to a divergent nuclear fission chain reaction.


uranium isotope with mass number 235 and half-life 7.13 X 108 years, fissionable with slow "thermal" energy neutrons and capable in a supercritical mass of sustaining a nuclear fission chain reaction that can proceed explosively with appropriate mechanical arrangements.

Highly U235 Enriched Uranium:

natural uranium modified by isotope separation (concentration) to increase the 0.7% occurrence of the U235 isotope to 93%; highly enriched uranium was employed as the fissionable material for the Mark I weapon detonated in combat at Hiroshima; highly enriched uranium contrasts with the slightly enriched uranium (approximately 20% U235) employed in the Mark II weapon which was proof fired at the Port Chicago Naval Magazine 17 July 1944.

naturally radioactive, silvery metallic transuranic element, occurring in natural uranium ores in negligible quantity and produced artificially by neutron bombardment of the uranium isotope U238; fifteen isotopes with masses ranging from 232 to 246 and half-lives from 20 minutes to 76 million years; used, especially the highly fissionable isotope Pu239, as a reactor fuel and in nuclear fission weapons; atomic number 94, melting point 639.5?C, boiling point 3,235?C. Discovered shortly after the element neptunium, and named by analogy after the planet Pluto, which is more distant from the sun than Neptune. The highly fissionable plutonium isotope Pu239 was employed in the Mark IV weapon tested in the New Mexico desert 16 July 1945, and detonated in combat at Nagasaki 9 August 1945.

Isotope Separation:

isolation of one isotope from an element in which it naturally occurs, or concentration of one isotope by the removal of unwanted isotopes from an element in which they occur. Since isotopes of the same element behave identically in chemical reactions, World War II separation of uranium isotopes was accomplished by mechanical methods, which depended on the different atomic weight of each isotope as determined by the number of neutrons in the nucleus of each isotope.

Liquid thermal diffusion uranium isotope separation:

the isotopes of natural uranium prepared in liquid and heated in a vertical column will separate by the ensuing rise, or diffusion, of the lighter isotopes to the top of the column and the settling of the heavier isotopes to the bottom; in this system the lighter, fissionable U235 isotope accumulates at the top of the column and the heavier, non-fissionable U238 isotope accumulates at the bottom.

Many such columns connected in series as a cascade process the partially U235 separated material drawn from the top of each preceding column to the next, so that the separation and accumulation of U235 is gradually increased in each column as the liquid material passes through the cascade. The process was developed by Philip Abelson, first at the United States Naval Research Laboratory and during the first six months of 1943 had produced the first separated U235 in weapon quantity.

Nuclear fission chain reaction:

self-replicating (divergent) nuclear reaction in which an atomic nucleus is split into fragments, usually two fragments of comparable mass, by the impingement of an energetic free moving neutron, with the release of one or more neutrons from the split nucleus, which may sustain or multiply the fission process in U235 or plutonium; the fission of each nucleus evolves 100 million to several hundred million electron volts of energy.

Mark I:

highly U235 enriched uranium gun assembly atomic bomb detonated in combat at Hiroshima, Japan, 6 August 1945, but not proof fired with active material prior to combat use; also known as Little Boy.

Mark II:

autocatalytic uranium hydride lateral implosion experimental device; previously undisclosed Manhattan Project cylindrical configuration U235 or plutonium atomic bomb design and technology which was precursor to Mark III; Mark II, a low-yield, tactical weapon, was certified 4 July 1944 to the Joint Chiefs of Staff for the purposes of operational planning, subject to the necessity of one proof firing before the Mark II could be available for combat use. The Port Chicago explosion which provided proof of the Mark II weapon determined the future development of Mark II; in consequence of the Port Chicago explosion Mark II was put on the shelf 17 August 1944, with agreement that the Mark II could be developed for combat use in 3 or 4 months time if required. Chief of Staff Gen. George C. Marshall planned the use of nine Mark II weapons, each with an anticipated energy yield equivalent to 1,000 tons of TNT, to prepare Japanese beaches and near-shore areas for an Allied invasion of the Japanese home islands if that invasion had been required. Two postwar experimental detonations of Mark II were conducted at the Nevada test site: Ruth and Ray of the 1953 Upshot-Knothole series.

Mark III:

first prototype spherical implosion atomic bomb design and technology susceptible to use with highly U235 enriched uranium or plutonium; did not use focused implosion technology; not proof fired with active material, and eliminated from practical development by assurance the markedly more efficient Mark IV bomb design would be practicable.

Mark IV:

improved the efficiency of the prototype Mark III spherical implosion design by application of focused implosion technology; susceptible to use with highly U235 enriched uranium or plutonium; with plutonium was proof fired at Trinity site, New Mexico, 16 July 1945 and detonated with plutonium in combat at Nagasaki, Japan, 9 August 1945; also known as Fat Man.

Atomic Bomb Military Policy Committee:

(Three members; one alternate.) Washington, DC, Carnegie Institution President Vannevar Bush, civilian committee member and committee chairman (deceased); Harvard University President James B. Conant, alternate civilian committee member and alternate committee chairman (deceased); Rear Admiral William R. Purnell, USN, Navy member (deceased); and General Wilhelm D. Styer, USA, Army member (deceased). President Franklin D. Roosevelt had designated Vice President Henry A. Wallace, Secretary of War Henry L. Stimson and Army Chief of Staff General George C. Marshall to have determination of general policy in the atomic bomb project who, on September 23, 1942, appointed the Military Policy Committee, and appointed General Leslie R. Groves the committee's executive officer. Constituted as above, the committee served through World War II.

Groves, General Leslie R., USA:
Commanding Officer, Manhattan Engineer District, United States Army Corps of Engineers; Executive Officer, Atomic Bomb Military Policy Committee (deceased).

Conant, James B.:
President Harvard University; principal science advisor to Gen. Groves; Atomic Bomb Military Policy Committee alternate civilian committee member and alternate committee chairman (deceased); provided Military Policy Committee liaison with Manhattan Project Los Alamos Laboratories via Los Alamos Laboratories Director J. Robert Oppenheimer and Military Policy Committee Executive Officer Gen. Groves.

Parsons, Rear Admiral William Sterling, USN:
as newly appointed Captain, USN, assigned duty at Los Alamos, May 1943, as director of the Ordnance Division; Associate Director, Los Alamos Laboratories, 1 August 1944; bomb commander Hiroshima mission, 6 August 1945; in chain of command reported to Adm. William R. Purnell, Military Policy Committee; technical director postwar Bikini and Eniwitok atomic bomb tests (deceased).

Reynolds, George T.:
Professor of Physics Emeritus, Princeton University; Manhattan Project Los Alamos Laboratories scientist as Ensign, United States Naval Reserve. With Capt. Parsons and Maurice M. Shapiro conducted extensive onsite investigations of the physical effects of the Port Chicago explosion in the immediate aftermath, which in comprehensive analysis were reported in several hundred pages transmitted by Capt. Parsons to Military Policy Committee member Adm. William R. Purnell between July 27, 1944 and October 1944 (surviving).

Shapiro, Maurice M.:

Chief Scientist Emeritus Laboratory for Cosmic Physics, United States Naval Research Laboratory; civilian Manhattan Project scientist at Los Alamos Laboratories who, with Capt. Parsons and Ens. Reynolds, conducted extensive onsite investigations of the physical effects of the Port Chicago explosion in the immediate aftermath, which were reported in several hundred pages of analysis transmitted by Capt. Parsons to Military Policy Committee member Adm. William R. Purnell between July 27, 1944 and October 1944 (surviving).

Ashworth, Vice Admiral Frederick L., USN:

career associate, friend and confidant of Capt. Parsons; assigned duty at Los Alamos Laboratories, autumn 1944, on recommendation of Adm. Purnell and Capt. Parsons, to whom then-Commander Ashworth reported; bomb commander Nagasaki mission, 9 August 1945; participated in postwar Bikini and Eniwitok atomic bomb tests as Adm. Parsons' executive officer; retired commander United States Navy 6th Fleet (surviving).

Oppenheimer, J. Robert:

Director Los Alamos Manhattan Project laboratories (deceased).

"History of 10,000 ton gadget":

document purloined, winter 1944-45, from the Manhattan Project Los Alamos Laboratories by photo technician Paul Masters; mathematical model prediction of the progression and effects of the explosion of the Mark IV weapon detonated 16 July 1945 at New Mexico Trinity site; prepared by Los Alamos scientists Joseph O. Hirschfelder and William G. Penney. Provides detailed technical specifications of Mark IV and, in the bottom line, predicts "Ball of fire mushroom out at 18,000' in typical Port Chicago fashion." Document recovered by the author among 1940s photo supplies donated by Paul Masters to the spring 1980 rummage sale of the Christ Evangelical Lutheran church, Santa Fe, New Mexico; published by the author, spring 1982.