[harshreality]

Does the U.S. make weapons-grade U235 anymore except for research? I thought gun-type fission weapons were phased out for safety and efficiency reasons. I also thought essentially all "fission" weapons today are fusion-boosted, and I thought the implosion type was the only production-ready design of fusion-boosted weapons.

[GemesAS]

The US isn't producing HEU anymore but still has a decent sized stockpile of it.

A number of the pits in the active stockpile are actually composite Pu/HEU pits & you can actually use HEU in implosion weapons as well.