LHTR: In step 7, combat continues unless one of the following conditions occurs (in this order of sequence):
Condition A) Attacker withdraws all attacking units;
Condition B) Defender withdraws all submarines by submerging, leaving no other defending units in play;
Condition C) Either or both sides lose all units.
So the attacker may withdraw before defending subs submerge.
Another nice tactic especially for Germany: If UK (or in same cases US) has a lot of BB (or even combined bombardement), doing attacks (opening fire) like 1 INF + many BB vs. GER or EEU. So GER normally loses a bunch of INFs every round with a value of over 8 IPCs. Then GER should build a SUB in BAL, in order to avoid this opening fire (sub-stalling). The BBs have to fight against the SUB an can´t do their opening fire for the battle in EEU or GER.
I don´t know whether this was already mentioned.
Bye,
Lili