Krieghund already explained that it is a problem of wording, the word selected “attack” should have been “surprise strike” or “surprise firing”, if I am not making a mistake.
I am not english born but I am considering that “surprise attack” has been not used to indicate the “attack” but the roll of the dice trying to hit the enemy. I do not see the need for a specification for the sub being in defense being able to perform a surprise strike. It is a sub ability to stay hidden and strike by surprise. It do not depend by the role in the battle, the sub is aiming to hit the enemy in both case, attack and defense, acting in the same way: lurking below the surface, hidden and dangerous.
given this logic, which I am not disputing, why then do subs defend at 1 and attack at 2? 🙂
same reason why fighters attack at 3 and defend at 4 😉