use Jumbo. Instead, it was placed in a steel tower about 800 yards
from ground zero. The blast destroyed the tower, but Jumbo survived
intact.

Today Jumbo rests at the entrance to ground zero so all can see it.
The ends are missing because, in 1946, the Army detonated eight 500-
pound bombs inside it. Because Jumbo was standing on end, the bombs
were stacked in the bottom and the asymmetry of the explosion blew the
ends off.

To calibrate the instruments which would be measuring the atomic
explosion and to practice a countdown, the Manhattan scientists ran a
simulated blast on May 7. They stacked 100 tons of TNT onto a 20-foot
wooden platform just southeast of ground zero. Louis Hemplemann
inserted a small amount of radioactive material from Hanford into
tubes running through the stack of crates. The scientists hoped to
get a feel for how the radiation might spread in the real test by
analyzing this test. The explosion destroyed the platform, leaving a
small crater with trace amounts of radiation in it.



Bomb Assembly


On July 12 the two hemispheres of plutonium were carried to the George
McDonald ranch house just two miles from ground zero. At the house,
Brig. Gen. Thomas Farrell, deputy to Maj. Gen. Leslie Groves, was
asked to sign a receipt for the plutonium. Farrell later said, "I
recall that I asked them if I was going to sign for it shouldn't I