Operation CASTLE Commander's Report (1954).
'The Bravo event of the CASTLE series yielded 15 megatons,
unexpectedly the most ever exploded in atmospheric testing by the
U.S.. A scientific miscalculation based on a then-unknown "tritium
fusion bonus" of highly enriched lithium-6 contributing the the
detonation yield caused the yield to be about two and a half times
of that what was expected.
Reports indicate that Bravo was the single worst incident of
fallout exposure in all of the U.S. atmospheric testing program.
Despite winds in an acceptable flow zone, the greatly unexpected
yield caused a much larger mushroom than originally calculated,
causing a much wider and massive accumulation path of fallout
danger. Fallout was scattered over more than 5,000 square miles of
ocean and islands, resulting in the contamination and exposure of
military, civilian U.S. personnel working on the shot, and people
of the islands who were earlier moved to a supposedly "safe" island
but received large amounts of radiation. Acute radiation effects
were observed among some of these people.'
http://www.archive.org/details/CastleCommandersReport1954
Hacker, Barton C.: Elements of controversy: the Atomic
Energy Commission and radiation safety in nuclear weapons testing,
1947-1974. University of California Press, 1994 - 614 pp.
Military Effects Studies on Operation CASTLE (1954).
http://www.archive.org/details/MilitaryEffectsStudiesonOperationCastle1954
United States Nuclear
Tests, July 1945 through September 1992. 
U.S. Department of Energy Nevada Operations Office, DOE/NV--209-REV
15, December 2000.