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
take it and handle it. So I took this heavy ball in my hand and I
felt it growing warm, I got a certain sense of its hidden power. It
wasn't a cold piece of metal, but it was really a piece of metal that
seemed to be working inside. Then maybe for the first time I began to
believe some of the fantastic tales the scientists had told about this
nuclear power."
At the McDonald ranch house the master bedroom had been turned into a
clean room for the assembly of the bomb core. According to Robert
Bacher, a member of the assembly team, they tried to use only tools
and materials from a special kit. Several of these kits existed and
some were already on their way to Tinian, the island in the Pacific
which was the base for the bombers. The idea was to test the
procedures and tools at Trinity as well as the bomb itself.
At one minute past midnight on Friday, July 13, the explosive assembly
left Los Alamos for Trinity Site. Later in the morning, assembly of
the plutonium core began. According to Raemer Schreiber, Robert
Bacher was the advisor and Marshall Holloway and Philip Morrison had
overall responsibility. Louis Slotin, Boyce McDaniel and Cyril Smith
were responsible for the mechanical assembly in the ranch house.
Later Holloway was responsible for the mechanical assembly at the
tower.
In the afternoon of the 13th the core was taken to ground zero for
insertion into the bomb mechanism.
The bomb was assembled under the tower on July 13. The plutonium core
was inserted into the device with some difficulty. On the first try
it stuck. After letting the temperatures of the plutonium and casing
equalize the core slid smoothly into place. Once the assembly was
complete many of the men took a welcome relief and went swimming in
the water tank east of the McDonald ranch house.
The next morning the entire bomb was raised to the top of the 100 foot
steel tower and placed in a small shelter. A crew then attached all
the detonators and by 5 p.m. it was complete.