@Young:
During the combat movement phase of G1, Germany attacks SZ #109 with, 1 u-boat, 1 fighter, 2 tactical bombers, and 1 strategic bomber, the allies scramble 3 fighters from London into the battle. During the resolve combat phase Germany hits with the u- boat, and 1 strategic bomber for a total of 2 hits (the hit from the sub must be applied to the destroyer, and the allies also choose to move a French fighter behind the casualty line).
For defense rolls, the UK misses with the destroyer but hits twice with fighters, now can Germany use the sub as a casualty even though the destroyer missed (I think so as long as there is a destroyer, subs can be used as casualties from hits by air units). In the next round, the sub will have nothing to hit because they can’t attack air units, and even though the air battle is still in progress, the sub can’t be hit by air units if their destroyer is off the board, is all this correct?
Actually, if you instead choose 2 air units as casualties on round 1, you can keep the sub in the battle and roll at the transport until it dies (it is not an autokill since a battle still rages)….this means losing more air units for Germany, but if you are going Sea Lion, trading air may not be a bad thing. Essentially, if you are OK losing your air units, you can get the transport even if the defender has air units scrambled so long as they removed the destroyer on round 1.
The point to rolling is that if you score a hit on round 2 with the sub and you have surviving air, you can retreat at the end of the round, thus giving you the transport sunk if that is your mission. Otherwise, you would fight until the Germans have no air units left, then to save time, remove the UK transport as any UK air will not save it from the subs eventual hit.