Lets just give it an ability that negates darkness/concealment on all its asw attacks. Adds value every turn and a distinctive edge over loitering asw options
I like that: then the acoustic torpedo is "built in" to the attack value in that the attack is good (ASW 3) and not affected at night (because it tracks sound, not sight).
University Student— Lover of Plato, Aristotle, War At Sea, Palestrina, and Mozart
Version 1 Liberator GR Mk III (Base Stats from B-24D Liberator) Patrol Bomber 1943
Bomb 5 Torpedo 1 Asw 3
A4 V7 H1 Defensive Armament Excellent Endurance ASW Torpedo: Once per game, instead of making an attack. Select a local enemy Submarine and roll a die. On a 5 the target takes 1 hull point of damage. On a 6, that unit takes 2 hull points of damage. This action ignores darkness and concealment.
Or Swap ASW torpedo for
Improved ASW: This unit ignores concealment and darkness when making ASW attacks.
Why make a new SA for a 33% chance to damage a sub? With the 3 ASw dice you have a 63% chance to damage it. If you really want to keep it KISS, just give it Submerged Shot. 1) Torpedoes already ignore darkness, 2) since you have to be in the same sector as the sub the torpedo would only miss on a roll of a 6 on a d6 for concealment, 3) you would then have a 16% chance of killing most subs out there with one shot in the Air phase vs. a 63% chance of damaging the sub during the air phase.
This makes the unit unique and doesn't add any new SA's while providing the feel you are looking for.
What about ASW Harassment? Submerged shot hits less than ASW 3 and doesn't give the submarine a penalty on its next torpedo attack. While I like Submerged Shot (it's not opg!), I think something else should be added to either make the torpedo attack more powerful (with a modified Combined Attack SA, Submarine Killer), or to make it penalise the submarine under attack (an ability that explicitly says: the attacked submarine is under ASW threat, or maybe an ability that forces the submarine to move, or lowers its armour.)
University Student— Lover of Plato, Aristotle, War At Sea, Palestrina, and Mozart
Which goes back to giving an ability negating concealment, including squalls, and darkness. A permanent, situational advantage in a reasonably controllable. Rather than a clunky exception, opg, in all circumstances
I prefer a permanent ASW advantage to a one time SA. There's no perfect way to simulate the acoustic torpedo in this game. Just go with the best option.