When Germany developed the V1 Flying bomb they must of had plans somewhere to launch a couple off a sub . Could they have built a ramp and fired one using compressed air? Granted they wouldn’t have done huge damage but it surely would have been a propganda victory.
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It wasn’t technically infeasible. The US Navy accomplished this shortly after the war:
https://en.wikipedia.org/wiki/Republic-Ford_JB-2
As with all things Wunderwaffe, it was a matter of time, timing, and resources. Of which, Nazi Germany was always missing at least one of those things. When they had the time and resources to pull it off the Nazis were too busy raping the hell out of Russia. By the time the Nazi high command realized that America’s involvement in the war was going to be an issue it was already too late.
A successful attack with a U-boat launched V-1 would have only ever been a Pyrrhic propaganda victory. Yes, a V-1 would have probably destroyed a building or two in NYC and killed a bunch of civilians but that would have only served to piss Americans off more than they already were at a time when USAAF bombers were blocking out the Sun in Berlin.