Accidents involving nuclear weapons have occurred almost since such weapons were first developed, and these events were a common occurrence during the Cold War. However, the US and other countries possessing nuclear arms developed various safety systems to prevent accidental thermonuclear reactions within these weapons even under the most extreme circumstances in order to avoid potential catastrophes. Even so, non-thermonuclear detonations of the conventional high explosives carried within nuclear weapons still pose a serious threat since they can spread dangerous radioactive contamination much like a so-called "dirty bomb." This scenario has occurred several times during aircraft accidents when high speed impacts or burning fuel caused the high explosive charges on nuclear weapons to ignite.

At least three dozen serious accidents and incidents involving atomic or nuclear weapons have occurred since 1950. Many of these cases cost the lives of military personnel, led to the release of radioactive material, or resulted in the loss of the weapon itself. Most of these weapons fell into the ocean where the nuclear material could not be recovered given the limits of current technology. It is estimated that over 50 nuclear warheads have been lost in the world's oceans following aircraft or naval accidents. Another 26 nuclear reactors from ships and submarines have also been lost or deliberately dumped at sea.