First atomic explosion. Computer coloured image of the detonation of the world's first atomic bomb (code name: Trinity) at Los Alamos, USA. The project to produce this atomic bomb was known as the Manhattan Project. The plutonium device was detonated at 5.29 am local time on 16 July 1945, and had an explosive power equivalent to 10,000 tons of TNT. The flash from the explosion could be seen 250 miles away, and the shock wave was felt 50 miles away. The details of the explosion were kept secret until after the destruction of Hiroshima on 6 August 1945. The army initially reported the explosion as "...an accident at an ammunition dump."