Mobilizing in hostile sea zones

[medmatt]

When new sea units are mobilized into a sea zone that contains enemy ships, combat does not occur based on the instructions. When the turn for the enemy ships comes up and the enemy ships choose to stay in the sea zone who is considered the attacker and the defender.

For example: Japan has one battleship and one carrier in sea zone 55. During the United States turn two destroyers are mobilized in sea zone 55 and no combat occurs. During Japan's next turn during the combat phase is Japan considered the attacker or the defender in sea zone 55.

[zooooma]

The attacker is the active player, in your example, Japan.

[Krieghund]

When new sea units are mobilized into a sea zone that contains enemy ships, combat does not occur based on the instructions. When the turn for the enemy ships comes up and the enemy ships choose to stay in the sea zone who is considered the attacker and the defender.

For example: Japan has one battleship and one carrier in sea zone 55. During the United States turn two destroyers are mobilized in sea zone 55 and no combat occurs. During Japan's next turn during the combat phase is Japan considered the attacker or the defender in sea zone 55.
Welcome, Medmatt!

Page 11 of the Operations Manual, under "Phase 3: Combat Move":
Exception: During this phase, you may move any of your units out if spaces containing enemy units that were there at the start of your turn. (This normally occurs only in sea zones.) Doing so allows you to end the units' combat move in a space that doesn't contain enemy units. Units that remain in spaces containing enemy units will initiate combat in the next phase.
Since the acting player (Japan in your example) is initiating combat, that player is considered to be the attacker.