This footage is from the movie "Trinity and Beyond", directed by Peter Kuran.
Operation Dominic I was a series nuclear test explosions conducted in 1962 and 1963 by the United States in the Pacific. This one was dropped from a B-52 bomber aircraft on the Christmas Island. Exact Date (1962-1963) and Yield unknown (a few megatons).
Ivy Mike was the first H Bomb test, it was exploded at 7.15 am local time on November 1st 1952. The mushroom cloud was 8 miles across and 27 miles high. The canopy was 100 miles wide. Radioactive mud fell out of the sky followed by heavy rain. 80 million tons of earth was vaporised. Mike was the first ever megaton yeild explosion.
