EVENT
OPERATION
1.
OAK was detonated on the reef nine miles north of Leroy Island,
Enivetok Atoll, at 0730M, 29 June 1958. The yield of 9 MI produced a
cloud which pierced the trepopause at 55,000 feet in vell under two minutes,
No actual observations on the initial cloud height were made because no
aircraft were in position; however, it is estimated that initial height
was probably near 78,000 feet. The first reading was obtained at Ht3
hours vhen a sampler afrcraft reported the stabilised height of the cloud
at 67,000 fect.
2.
Initial movement of the lower portion (below 50,000 feet) was
te the west, with a net velocity of slightly over fifteen knots.
The
lagoon vas swept with more than usual caution due to the size of the
detonation.
Re-entry hour was declared et 1000M after a thorough P2V
sweep at 1,000 feet.
The atoll was free of contamination except for the
islands Alice through Daisy (closest to grofind sero), which averaged 35 mr.
3. The portion of the cloud at approximately 55,000 feet remained
in the vicinity of ground zero for several hours, then moved ‘slowly to
the southwest. This cell was reported 60 miles southwest at nightfall
with an intensity of 350 mr/hr measured by the sampler aircraft,
This
cloud was again detected early the next morning at 200 miles southwest of
(iis
Fred and was measured at 40 ur/hr. No further information on this part
of the cloud became available.
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TAB A
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