All current nuclear weapons are test by simulation on petaFLOPS supercomputers at the US labs.
Only on test sites.
Bikini Atoll in the Marshal island chain .
All the facilities used by the US to prepare the materials for nuclear weapons, build nuclear weapons, design and test new nuclear weapons. This is all lead by the Department Of Energy.
The last U.S. above-ground (atmospheric) test was in 1963. The last U.S. underground test was in 1992. The Comprehensive Test Ban Treaty (signed by many major powers) ended testeing of all kinds, atmospheric or underground, in 1992. The U.S. models (with supercomputers) characteristics of nuclear weapons 'explosions' in order to 'test' its weapons designs.
The difference was that the US could test and improve it's weapons/equipment; the Soviets couldn't. But they could observe. Translation: Secret weapons weren't secret no more.
Most US weapons of any kind are made in the US.
Both the US and USSR had deliverable nuclear weapons in the 10+ megaton range by 1955.
US weren't effected by the Nuclear Weapons, They created it.
The UK was the third country to obtain nuclear weapons, after the US and the USSR. The UK had its first successful nuclear weapon test in October 1952, a plutonium warhead similar to the one dropped on Nagasaki.
Soldier, test fire your weapons now!
The US first stockpiled chemical weapons during the 1930s.