Modern torpedoes are not like what you see in the movies (at least not all the torps).
Modern torpedoes can troll at lower speeds with virtually no acoustic signature, and then sprint the final 150/200m when there is little or no defense. Also, even if the SKs DID hear “high speed screws” there is little they could do in time.
Secondly, this occurred in relatively shallow water and the acoustics would be pretty lousy for a SONAR operator — lotsa surface noise, the sound of their own screws, etc.
Most likely though the sub was close enough that when torpedo went to high speed, there was no chance of counter measures or effective maneuvering.
Torps are much faster than a ‘corvette’ like this.
I knew about the torps but did not consider the shallow area. Thanks.
I think it likely that there is no ASW gear aboard this small vessel. The torp would never have been detected. Nor would a mine.