by the nuclear reaction. One radioactive isotope in the fallout,
iodine-131, rapidly built up to serious concentration in the thyroid glands
of the victims, particularly young Rongelapese children.

More than any other event in the decade of testing large nuclear weapons in
the atmosphere, Castle/Bravo's unexpected contamination of 7,000 square
miles of the Pacific Ocean dramatically illustrated how large-scale nuclear
war could produce casualties on a colossal scale, far beyond the local
effects of blast and fire alone.

A number of other surprises were encountered during 30 years of nuclear
weapons development. For example, what was probably man's most extensive
modification of the global environment to date occurred in September 1962,
when a nuclear device was detonated 250 miles above Johnson Island. The
1.4-megaton burst produced an artificial belt of charged particles trapped
in the earth's magnetic field. Though 98 percent of these particles were
removed by natural processes after the first year, traces could be detected
6 or 7 years later. A number of satellites in low earth orbit at the time
of the burst suffered severe electronic damage resulting in malfunctions
and early failure. It became obvious that man now had the power to make
long term changes in his near-space environment.

Another unexpected effect of high-altitude bursts was the blackout of
high-frequency radio communications. Disruption of the ionosphere (which
reflects radio signals back to the earth) by nuclear bursts over the
Pacific has wiped out long-distance radio communications for hours at
distances of up to 600 miles from the burst point.

Yet another surprise was the discovery that electromagnetic pulses can play
havoc with electrical equipment itself, including some in command systems