It's amazing how bad many nuclear weapons were, and perhaps are. The Hiroshima gun bomb wasn't much better than an IED. If the Enola Gay had crashed, it probably would have gone off. (The crew was under orders not to land with the bomb; if they had to return to base, they were to dump it in deep water.)
For a while after WWII, the US didn't actually have any functional nuclear weapons. This was a major secret at the time. The war designs weren't suited for long-term storage. Nobody wanted another gun bomb, and the first generation electronics for triggering implosion didn't store well. A "GI-proof" line of bombs had to be developed.
The first round of Polaris missile warhead wouldn't have worked. This was learned only after there were SSBNs at sea with functional missiles and dud warheads. That took over a year to fix.
In recent years, there was a period for over a decade when the US had lost the ability to make new fusion bombs. The plant to make some obscure material had been shut down, and the proposed, cheaper replacement didn't work.
There was a tritium shortage for years. The old tritium production reactors were shut down years ago, and no replacement was built. The US is now producing tritium using a TVA power reactor loaded with some special fuel rods. Commercial use of tritium (exit signs and such) is way down from previous decades. (Tritium has a half-life of around 11 years, so tritium light sources do run down.)
The US was the last country with a gaseous-diffusion enrichment plant. The huge WWII-vintage plant at Oak Ridge was finally dismantled a few years ago. There's a centrifuge plant in the US, privately run by URENCO, a European company.
The US had a huge buildup of nuclear capability in the 1950s, and most of the plants date from that era. They're worn out and obsolete.
And that's the stuff we know about. Being a nuclear superpower isn't cheap.
