@Young:
That would mean that a single submarine can block an amphibious assault from happening, which dosen’t seem accurate. If you are in fact correct, that would make this rule broken.
It may not seem accurate, but it’s in the same line as one destroyer stopping a whole fleet from moving two spaces or from being able to do shore bombardment.
And yes, you could attack the cruiser and destroy it with the planes and then during non-combat your transports could ignore the remaining sub. However, also note that although the carrier has no attack value and the planes can’t hit subs, the sub can still hit the carrier, so it doesn’t make sense that you could keep it out of battle when it could do damage. But yes, once the cruiser is destroyed by the planes and the carrier is destroyed by the sub, only the planes and sub are left and the sub can still sink the transports.