Pure fission weapons historically have been the first type to be built by a nation state.

The idea came to Ulam while studying some aspects of fission weapons.

It was the largest pure fission weapon ever deployed by any nuclear state.

But the general principles for making a fission weapon are widely known among scientists.

For the remainder of the war, however, the effort was focused on first developing fission weapons.

Such material could be used in fission weapons capable of destroying entire cities.

The Mark 5 and W5 were a pure fission weapon.

"They are not known to carry fission weapons, but that is a more likely possibility."

Oppenheimer felt that resources would be better spent creating a large force of fission weapons.

A related military use of the word is in describing gun-type fission weapon.