I do not see a specific mention of this. The closest is the sidebar on page 19 of the rulebook.
I would see no reason why the subs could not fire at the transports they are a valid target for the subs. The attacking planes would have to kill the defending planes first before targeting the transport.
I believe you need to capture the sea zone before you can kill any defending transports.
Wasn’t the rule that transports have to be hit last. Well if air is an illegal target for a sub, then the last target is the transport. So the sub should hit the transports. Its then up to enemy air to kill the sub before it kills all the transports one at a time.
Correct, except that the defending fighters can’t hit the subs because there’s no defending destroyer.
The bottom line is that the transports are toast and the subs are safe. The only fighting left is between the fighters.
Here’s the thing about the defenseless transport rule: Imagine that the transports are rolling dice just like everything else, only they need a zero to hit. Since there are no zeroes on the dice, they will never hit. Any battle involving transports plays out like any other battle, with two exceptions. One is that the transports may only be taken as a casualty when there is no other choice. The other is that when it gets to the point where the only dice being rolled on one side need a zero to hit and dice that can hit are still being rolled on the other side, and it’s only a matter of time before the transports are destroyed, you can stop rolling dice and remove the transports. The sole point of the rule is to keep you from rolling endless dice until you kill all the transports.
Technically, in the example above the fighters will continue to roll back and forth until one or both side’s fighters are gone. In the meantime, the subs will continue to roll and remove a transport every time they hit. If there are still transports remaining when the fighters are done, they will be automatically removed, since the subs can keep rolling until the end of time until the transports are destroyed.