From: Palo Alto, CA
You can only attempt to intercept naval units you are at war with. If several major powers’ or minor country’s units attempt to intercept a task force containing units from the other side, you don’t all have to be at war with every moving unit to intercept the task force ~ however the naval units not at war with any intercepting major power or minor country are ignored in the subsequent naval combat.
During port strikes and naval combats, a unit can’t fight against units from the other side unless it is at war with at least one of them (being at war with an enemy unit the naval unit is transporting is not enough). However, you resolve, as one combat, a combat that includes units that are not at war with each other, so long as each unit included is at war with at least 1 enemy unit in the combat.
Example: A combat includes a Commonwealth and a US naval unit against a Japanese and a German unit. The US is at war with Japan and the Commonwealth is at war with Germany. You fight this as one combat even though US units can’t fight Germans and Japanese units can’t fight Commonwealth. The Japanese unit is sunk. In the next round, the US unit isn’t included because it can’t fight German units.
Exceptions to the restriction on neutral naval units fighting are US units escorting Allied convoys (see 13.3.2, entry options 11, 29 & 38) and all US units after unrestricted naval warfare is chosen (entry option 50).
However a lone naval unit, regardless of cargo, cannot be attacked unless you are at war with the owner of the ship.
Now that Ive said this, I have no proof, but expect to be exonerated
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