December 5, 1965 -- Pacific Ocean
An A-4E Skyhawk attack aircraft loaded with one B43 nuclear weapon rolled off the deck of the USS Ticonderoga while the aircraft carrier was traveling from operations off Vietnam to Yokosuka, Japan. The plane and its pilot sank in 16,200 feet of water. Pilot, plane and weapon were never found. The U.S. Defense Department reported the incident took place "more than 500 miles from land." But Greenpeace, quoting U.S. Navy documents, said the accident occurred about 80 miles east of the Japanese Ryuku Island chain and about 200 miles east of Okinawa.
(Sources: Greenpeace; U.S. Defense Department)