Nation: MILESTONES IN NUCLEAR HISTORY

JULY 16, 1945—World's first atomic explosion, by U.S., at Alamogordo, N. Mex.

AUG. 6, 1945—Atomic bomb dropped by U.S., on Hiroshima, Japan.

AUG. 9, 1945—Second atomic bomb dropped by U.S., on Nagasaki, Japan.

JULY 1 AND JULY 25, 1946—First test series, Operations Crossroads, at Bikini.

AUG. 29, 1949—First Soviet atomic explosion, ending U.S. monopoly.

NOV. 1, 1952—World's first hydrogen bomb explosion, by U.S., in Operation Ivy near Eniwetok.

AUG. 12, 1953—First Soviet hydrogen bomb explosion.

MARCH 1, 1954—Biggest U.S. explosion on record (15 megatons). Operation Castle, showers radioactive ash beyond safety zone, burns 23 Japanese fishermen.

OCT. 31, 1958—U.S. begins test moratorium. Russia follows three days later.

SEPT. 1, 1961—Russia...