This Day in History - Hydrogen Bomb

From historychannel.com:

1956 United States drops hydrogen bomb over Bikini Atoll

The United States conducts the first airborne test of an improved hydrogen bomb, dropping it from a plane over the tiny island of Namu in the Bikini Atoll in the Pacific Ocean. The successful test indicated that hydrogen bombs were viable airborne weapons and that the arms race had taken another giant leap forward."
[...]

The hydrogen bomb dropped over Bikini Atoll was carried by a B-52 bomber and released at an altitude of more than 50,000 feet. The device exploded at about 15,000 feet. This bomb was far more powerful than those previously tested and was estimated to be 15 megatons or larger ... Observers said that the fireball caused by the explosion measured at least four miles in diameter and was brighter than the light from 500 suns.

4 miles. That is a BIG-ass mushroom.