Also, the comintern was historically much better at exploiting social angles in the intelligence department, with the US mostly catching up thanks to technological advantage.But would the Reds really do the British working class that dirty? I feel like they'd pick somewhere like East Anglia, it's out of the way and a Tory heartland to boot, shows they're willing to consider their targets carefully.
Also, if the Reds do get the Bomb first, will the Americans be able to steal it as effectively as it was stolen from them? Communism is a better fifth-column recruitment system than... mild non-fascist American conservatism. It just seems like it would be harder for America to really call out to the Red's Theodore Halls and Klaus Fuchses and propel them to do something as risky as crossing the Comintern.
As for the bomb, probably aim at a military/naval base?