@Constantinople:
How have the subs rules changed from AAR?
Subs now cost 6 IPCs instead of 8.
The definition of a hostile sea zone has changed to a sea zone containing enemy surface warships. Surface warships are battleships, carriers, cruisers and destroyers. Subs are warships, but they are not surface warships. Transports are not warships at all. As a result, sea zones containing only enemy subs and/or transports are now considered friendly. This has several effects.
Subs no longer block movement of enemy ships. Ships can move though sea zones containing only enemy subs (or transports) as though they weren’t there. If they end a combat move in a such a sea zone, they can either attack the subs (or transports) or ignore them. In the case of an amphibious assault, attacking them will disallow offshore bombardment, while ignoring them will allow it. If a sea zone contains both enemy subs and surface warships, the subs can’t be ignored.
If a ship finds itself in a sea zone containing only enemy subs (or transports) at the beginning of its turn, no action is required. The ship has the option to stay there and attack, stay there and do nothing, move away during combat movement and attack somewhere else, or move away during noncombat movement.
Subs’ movement can only be blocked by enemy destroyers. Subs can end either combat or noncombat movement in a hostile sea zone. If combat movement ends in a hostile sea zone, combat ensues. Just as other ships can, they can attack or ignore enemy subs (or transports).
Subs no longer prevent enemy transports from loading if they are in the same sea zone. Sub-stalling is dead.
There are also some changes in subs’ combat abilities. They now defend on a 1. In combat, air unit hits can’t be assigned to subs unless there is a destroyer friendly to the air units in the battle.
Just as in AAR, a single enemy DD will cancel most sub special abilities. Subs still fire before everything else if no enemy DD is present, and their casulaties are removed immediately. However, since there is no Opening Fire step anymore, they fire with everything else if there is an enemy DD present.
Submerging is now done at the beginning of the combat round. A sub (attacking or defending) may submerge instead of firing. Attacking subs choose first, then defending. The presence of an enemy DD still cancels this ability. This means that subs can submerge before any shots are fired unless there is an opposing DD. Submerging simply means that they’re removed from the battle board and placed back in the contested sea zone, and there is no impact on the game beyond that.