During the Cold War, the films were highly classified, but now anyone can watch a newly released treasure trove of U.S. nuclear weapons tests on YouTube.

Greg Spriggs, a physicist at Lawrence Livermore National Laboratory in California, said the 750 movies were in danger of becoming degraded to the point that they were no longer useful.

“We got to this project just in time,” he said in a three-minute recording introducing the nuclear test videos. “We know that these films are on the brink of decomposing to the point where they become useless.”

The videos were taken in the 1950s and 1960s as part of tests on types of atomic blasts and to make predictions about damage during a potential nuclear war.

Data and observations from many of the tests are still valuable to researchers today.

“We’ve scanned a little over 4,200 films,” said Spriggs. “The only data we have are these old tests.”

The United States and then-Soviet Union tested thousands of nuclear bombs, including in the atmosphere, on the ground, underground and underwater during the Cold War. The U.S. conducted its last test in 1992 after the fall of the USSR.