A set of 62 rare videos of nuclear weapons tests have been uploaded to YouTube by the Lawrence Livermore National Laboratory. The declassified footage of mushroom clouds was captured on film more than 50 years ago.

The Laboratory, a federally funded research facility, has undertaken a project to digitize the classified films for preservation and to reanalyze the explosions for more accurate testing data. Weapon physicist Greg Spriggs and Jim Moye, a film expert, have been tasked with getting the footage off of the celluloid film it was shot on before it rots away.

“It’s fascinating to watch film that hasn’t been seen in more than 50 years,” said Moye in a statement. “This may be our one and only chance to preserve this historical record. It’s critical that we capture as much of the data as possible. I truly feel like we’re preserving history.”

The films were shot between 1945 and 1962 when the United States conducted 210 atmospheric nuclear weapons tests. These test exhibit the large mushroom clouds. The U.S. signed a treaty with the then Soviet Union in 1962 banning above-ground nuclear weapons tests. China was the last country to conduct an atmospheric nuclear weapon test in 1980, but North Korea has threatened one this year.

Spriggs estimated that there around 7,000 films in total and that the California Laboratory has scanned 4,500 of them. Around 750 of the films have been declassified and 64 of them were restored and uploaded to YouTube in March and another 62 were uploaded Thursday. Each nuclear test would be filmed with more than 50 cameras.

“We’ve received a lot of demand for these videos and the public has a right to see this footage,” said Spriggs in a statement. “Not only are we preserving history, but we’re getting much more consistent answers with our calculations.”