Some of what I've read (Human Smoke being one recent example) implies that 'The bomber will always get through' was a belief held by FDR, WC and many others and the bombing of Germany and Japan as a way to win the war were considered a very, very good option (take the war to the civilians - show them what the horror of total war is etc). So much so that when it wasn't working there was a great deal of pressure to say that it was working and would work.
The B-17, bought from the US... The RAF (trying to show bombing would work) tried it - flying high enough to keep away from too many fighters it could not carry many bombs, needed a lot of crew. Fly low - attracted too many fighters. At this time before the US was trying to bomb in daylight over Europe, the US was saying 'Oh - fly lower - fly more planes in and use covering fire - easy peasy lemon squeazy.' Which as we know turned out to be not a good idea at all. But remember - as with all things the 'Management' bring out - you have to be very careful how you disagree with it.
So then the RAF had a bunch of planes that it couldn't bomb Europe with but could fly about and look for submarines and such. Hence it got that job. Fair comment?