In 1950, an American B-36 bomber on a peace-time training mission crashed over British Columbia, Canada carrying a Mark IV atomic bomb, a weapon comparable in size to the nuke dropped on Nagasaki in 1945. According to testimonies from the surviving crew members, they had safely jettisoned the bomb, and detonated it in mid-air before the plane went down.

The crash became famous as the very first “broken arrow,” the U.S. military’s term for an accident involving a nuclear weapon. But questions swirled for decades about whether the bomb was really detonated over the ocean—or whether it went missing somewhere in the Canadian wilderness.

Five years after using the first atomic weapons to force the surrender of Japan in World War II, the United States military was preparing for a new era of nuclear warfare with its Cold War adversary, the Soviet Union. The Convair B-36 “Peacemaker” was the first true intercontinental bomber capable of carrying nuclear weapons to any part of the world, and the U.S. Strategic Air Command (SAC) was eager to test the new planes with a real payload.

A test bombing run goes awry

After months of lobbying, SAC leaders were able to convince the Atomic Energy Commission to lend them a Mark IV atomic bomb without its plutonium core. The bomb still contained large amounts of uranium and conventional explosives—but it couldn’t trigger a devastating nuclear blast.