@CptnKeener:
1. With no destroyer present - Do they only fire ONCE while in battle?
Once per round. If there is no destroyer, they fire in step 2, otherwise they fire in step 3 or 4. Steps 2-6 occur in each combat round.
@CptnKeener:
If a sub hits, can another sub be taken as a casuality?
Yes.
@CptnKeener:
2. If sub attacks sub, do they only fire at each other once or does battle continue for more than one round?
The battle continues until one is hit or submerges.
@CptnKeener:
3. With no destroyer present - If sub fires, and misses, does the opponent get to fire back at all?
Yes.
@CptnKeener:
If sub DOES hit and destroys the only target, I understand that the opponent does not get to fire back, an I understanding incorrectly?
Any ship sunk by a sub with no friendly destroyer present does not return fire, unless it’s a sub. Since sub fire is simultaneous, two subs can sink each other.