Torpedoes from ASW aircraft were not wasted; they were the best weapon they had.

See
http://en.wikipedia.org/wiki/Mark_24_Mine
FIDO was more effective than depth charges, achieving a 22% success rate vs. 9% for DCs.
The Allies spent millions developing - and the Germans lost 37 u-boats to - the acoustic FIDO torpedo late in the war.
German radar detectors were good enough that the boats coulds get under well before the aircraft arrived, but the FIDO pursued them underwater, tracking the noise they made on the crash dive. A hit at any depth was a virtually certain kill.