1950 Rivière-du-Loup B-50 nuclear weapon loss incident

The 1950 Rivière-du-Loup B-50 nuclear weapon loss incident refers to loss of a nuclear weapon near Rivière-du-Loup, Québec during the fall of 1950. The bomb was released due to engine troubles, and then was destroyed in a non-nuclear detonation before it hit the ground.

Background
Returning one of several US Mark 4 nuclear bombs secretly deployed in Canada, a USAF Boeing B-50 Superfortress had engine trouble and jettisoned the weapon at 10500 ft. The crew set the bomb to self-destruct at 2500 ft, and released it over the St. Lawrence River. The non-nuclear explosion shook area residents and scattered nearly 100 lb of moderately radioactive uranium (U-238) used in the weapon's tamper. The plutonium core ("pit"), which is the key component for a nuclear reaction and detonation, was not installed in the bomb at the time. The absence of the core probably was due to their cost and relative scarcity at the time.

At the time of the incident, the aircraft was returning from CFB Goose Bay to Davis–Monthan Air Force Base. The troubled aircraft successfully landed at an Air Force Base in Maine.

The incident was immediately covered up at the time, and explained away as 500 lb military practice bombs being detonated. It was not until the 1980s that the Air Force confirmed it was a nuclear incident.