There was a pre-test explosion of 100 tons of TNT on May 7 to calibrate the instrumentation. For the actual test, the plutonium core device, nicknamed the gadget, was placed on the top of a 20-metre steel tower for detonation. It had been assembled at the nearby McDonald Ranch House, the components arriving on July 12. It was assembled on the 13th and winched up the tower the following day. In case of failure, a huge steel canister code-named "Jumbo" was prepared to recover the plutonium; it was shipped to the test site but not used. The detonation was planned for 4 a.m. but postponed due to poor weather.
At 5:29:45 a.m. local time (Mountain War Time), the device exploded with a force equivalent to 19 kilotons of TNT. It left a crater in the desert 3 metres deep and 330 metres wide. The shock wave was felt over 160 km away, and the mushroom cloud reached 12,000 m. In the crater the silica of the desert melted and became glass of a light green colour, named trinitite. The crater was filled in soon after the test. The military reported it as a accidental explosion at a munitions dump, and the actual cause was not publicly acknowledged until August 6.