i'm guessing it took off from france, thus avoiding brittish radar, and i assume the americans didn't use radar 'cos whet with all their bigheadedness, they thaught no-one could get accross the atlantic, and as for the convoys, aslong as it wasn't bothering you, you left it alone in case it did attack you, but if you didn't hurt them, there's a chance they won't hurt you..................
well, that would be the typical american attitude wouldnt it!