@shadowhawk “In non-combat it’s not legal to do moves that could result in combat. Your moving sub into a hostile seazone.” == not correct.
“Unlike other sea units, submarines can move through and even into hostile sea zones in the Noncombat Move phase. However, a submarine must end its movement when it enters a sea zone containing one or more enemy destroyers.”
Why would you want to do this?
To disrupt the loading/unloading of troops and convoy ops.
Example: Allies own Java with transports and navy in the SZ 42 (Java waters). Japan sneaks a sub to SZ42 on non-combat. On the US turn, they wanted to take the inf in Java to defend Philippines but they want to use the DD to kill the sub. Here’s the problem, the amphib movement is a non-combat (US owns Philippines in this scenario) so the transport can’t move until the non-combat phase. However, if the DD attacks, all units in SZ42 at the time of combat are considered to be part of the attack, so the transport would be an “attacker” and at the end of combat would have it’s movement expended. Thus, either the transport leaves the area and could amphib attack some other hostile territory as this would be combat movement, or just hangout around Phillippines WITHOUT unloading.
Or, the US DD doesn’t attack the sub, it lives and gets to convoy Java.
Of course, this kind of situation is not common. But it is a consideration
Exact wording of applicable rule:
If your units are sharing a sea zone with only enemy submarines and/or transports (a friendly sea zone) and you want to ignore them, the normal rules of combat movement apply. However, if they are sharing a sea zone with enemy surface warships (a hostile sea zone), or you are attacking enemy submarines and/or transports there, each of your units must do one of the following:
Remain in the sea zone and conduct combat,
Leave the sea zone, load units if desired, and conduct combat elsewhere,
Leave the sea zone, either to load units or to establish a retreat route, and return to the same sea zone to conduct combat, or
Leave the sea zone and conduct no combat
Remember, you can only load units in friendly sea zones, so if this sea zone is hostile, you must load them elsewhere.
Once these sea units have moved and/or participated in combat, they can’t move or participate in the Noncombat Move phase of the turn.