Well, here's one: the Fritz X guided bomb.
I know some would say, but Hans, it was the first guided anti-ship bomb! It was genius! And it sunk the RM ROMA!
But hear me out the idea was indeed great. The execution... eh... not really.
The bomb required the plane to fly in a straight line for a rather long time, while the bombardier remote controlled the missile. Guess what ships had by then? AA guns. Speaking as an AA guy, guess what idea we LOVED the most? Planes flying in a straight line at constant speed. Guess what fighter planes love? The same.
Anyway, the Roma was the ONLY ship it ever sunk, and she wasn't exactly gunning back. And there was one other non-fatal hit. Any other plane carrying one got pwned with prejudice by AA and/or fighter planes. HUNDREDS of them. Being sent to drop one was just a tiny bit safer than being "volunteered" as kamikaze in Japan, but not by much, and with significantly less chances of achieving anything with your death.