The plutonium hemispheres for the pit of the Trinity nuclear test " gadget " ( bomb ) were delivered to the McDonald Ranch House on July 11 , 1945 . Brigadier General Thomas F. Farrell , the Deputy Director of the Manhattan Project , signed for them , and handed them over to Louis Slotin , the head of the Pit Assembly Team . The active components of the bomb were assembled in the assembly room on July 13 , 1945 , The bomb was winched up the test tower the following day . The Trinity test occurred on July 16 , 1945 . A plutonium Fat Man-type bomb was detonated , similar to the bomb later dropped on Nagasaki
Trinity nuclear test
Trinity (nuclear test)
McDonald Ranch House