@Sir_Cala:
A submarine either attacks or submerge.
If it attacks and hits a unit with a surprise strike with no destroyer present. The ship that is chosen to be hit does not defend and is removed from the battle board. Exceptions are Battleships. They take 2 hits and the second hit removes it off the battle board.
Repeat steps 2-7 if combat continues.
If a submarine submerges it is not involved in any sea battle.
well this was the reply directly above the post of the information from the rulebook which would hopefully make you understand the process.
I will even can go further in the explanation.
You cannot use surprise strike then submerge in the same combat sequence to avoid being fired upon.
If you choose surprise strike you will be fired upon if any other ships remain on the battle board after your sub fires.
Your subs fire first in step 2.
If your surprise strike attack hits it eliminates an opponents ship and it cannot fire back in step 3 or 4.
That is the benefit of surprise strike.
General Combat Sequence
Combat takes place over a number of rounds. Each battle round consists of several steps.
1. Place units along the battle strip
2. Submarine surprise strike or submerge (sea battles only)
3. Attacking units fire
4. Defending units fire
5. Remove defender�s casualties
6. Press attack or retreat
7. Conclude combat
Can a sub surprise strike another sub? Yes
Subs can use its surprise strike another sub and they both fire in step 2. However if the attacker hits the defending sub 1st the defending sub is moved to the casualty strip gets to fire back and is not eliminated until the end of step 2.