They risked their lives to capture on film hundreds of blinding flashes, rising fireballs and mushroom clouds.

The blast from one detonation hurled a man and his camera into a ditch. When he got up, a second wave knocked him down again.

Then there was radiation.

While many of the scientists who made atom bombs during the cold war became famous, the men who filmed what happened when those bombs were detonated made up a secret corps.

Their existence and the nature of their work has emerged from the shadows only since the federal government began a concerted effort to declassify their films about a dozen years ago. In all, the atomic moviemakers fashioned 6,500 secret films, according to federal officials.