On this date in 1957, five Air Force volunteers and one photographer stood next to a sign labeled “Ground Zero. Population: 5” and watched a two-kiloton nuclear bomb explode 18,500 feet over their heads. (The height listed at the beginning of the video is incorrect.) Before the dangers of radiation exposure were fully understood, the government undertook many such tests to determine the effects of atomic weapons. This particular trial was an attempt to prove that exploding nuclear missiles in the atmosphere could be relatively safe. While the men in this video were not greatly affected by the blast—at least three, including the cameraman, lived past age 80—many other people exposed to fallout from nuclear tests developed cancer. Check out the full story behind the video at NPR.