Admittedly not using sonar, but what about Antrim Flight (dear old pinger Stanley) double depth charging the Argentinian submarine Santa Fe and forcing it to return to South Georgia, leaking like a sieve? The AS12 attack by Endurance's Wasp did blow someone's leg off I believe. The Mk 46 torpedo attack failed. It's all there in Chris Parry's book.
In a wider context, how often have submarines and anti-submarine helicopters been pitted against each other in a war setting, say since the 1960s? I seem to remember plenty of times where it happened in exercises but then we knew there was actually a submarine there. I find it hard to think of an real war situation where the two have been pitted against each other. There was plenty of a/s pinging in the Falklands but I have no idea of whether Argentinian subs were actually present apart from at South Georgia.
NDBs were oh so secret at the time but a near certain kamikaze mission if used in anger. We even flew a circuit at Culdrose with one strapped on during an inspection, but at night in case anyone saw us!