why? no it wasn't the heaviest but bombing by day we'd get the P-51 escorts (surely if were're just swapping the planes we should just swap the planes not what comes with them) the the B-17's main escort was their escorts, not their defensive firepower, even the B-17's guns were useless if she was unescorted..........
and the yanks would have to give their tactics some serious revision, you can't fly in tight formations by night, and american radar technology was behind britain's, which would include the ground radar you want to fit to these B-17s, don't get me wrong i'm not saying they couldn't bomb at not, it's just they wouldn't be as good as the brits...................