How does the submerge rule work?
Immediately before you roll dice for submarine attacks, you decide which subs (if any) wish to fight, and which will submerge. Some can submerge while others stay and fight. For example, if some of your defending subs were hit by attacking units, it doesn’t make sense for them to submerge; they might as well take their final shot before sinking. Undamaged subs can submerge while damaged ones remain and shoot back. It doesn’t matter whether your subs are attacking or defending, they always have the option to submerge provided they haven’t yet rolled an attack in this combat round. They can even submerge before the first attack; that is, you can move subs into an enemy-occupied area and immediately submerge, preventing any combat from occurring (sometimes called sub-stalling). Once submerged, they are out of the battle for good.
