TIL that in 1956 a B-47 stratojet carrying two capsules of nuclear weapons material disappeared over the Mediterranean Sea and was never found.

https://en.wikipedia.org/wiki/1956_B-47_disappearance

https://www.reddit.com/r/todayilearned/comments/15pjps1/til_that_in_1956_a_b47_stratojet_carrying_two/