3. A U.S. Air Force nuclear bomber nose-dived during a training exercise over Ohio
On July 13, 1950, a USAF B-50 bomber from Biggs Air Force Base, Texas, flew over Lebanon, Ohio, during a routine training mission. Despite clear weather conditions, at 7,000 feet the bomber suddenly nosed down and flew directly into the ground. The bomber was carrying a nuclear weapon containing large amounts of high-explosives, but did not contain a fissile core. The resultant explosion was recorded as creating a crater 25 feet deep and 200 square feet in area, as well as being felt over 25 miles away by civilians.
No specific reason was identified for this sudden disaster, with attributions typically speculating catastrophic mechanical or engineering malfunctions as the most likely causes. Four officers and twelve airmen were killed in the incident, including all those aboard the crashed bomber.