Cards provide the detection levels or the detection countermeasures. The higher the detection level the better and harder the attacks become. If a sub detects a surface ships he's the only one who has the detection marker raised. If ANY member of a surface group detects a sub ALL members of the surface group raise their detection levels on the sub. This one isn't quite as fast and furious as GMT's Rise of the Luftwaffe but you can run several battles in an evening.
Sub is a card game.
What AS does provide is the cat and mouse feel of submarine combat, without the long boring periods of time between detections. Once the detection levels build I have found that the play gets just as exciting. The attacker is trying to increase the detection level or launch weapons, while the target is frantically trying to reduce the level, or evade the torpedos. Of course I have seen other games where the sub quietly builds up the detection level, puts a load of torpedos into the carrier and slips away. Very realistic, but somewhat boring.