Just as other ships may, submarines may also move out of a sea zone where they begin their turn with enemy ships, even destroyers. The destroyer doesn’t stop the sub’s movement, as the sub didn’t enter the sea zone - it started off there.
Put that in the FAQ
OK, so this whole debate arises from the rule that tells you to place one of your control markers under your AA gun if you move it into a territory controlled by a friendly power, correct? There is no corresponding rule that says that if I capture your AA gun when I capture your territory you should place one of your control markers under it. So, we have one fairly rare circumstance when I can capture your gun when it has your marker (in your ally’s territory) and another far more common one when I can capture your gun when it doesn’t have your marker (in your territory). In neither case am I directed to retain the existing marker or place a new one.
In addition, the rules indicate that if you or your ally recapture the territory and AA gun, the ownership of both goes to the capturing power, or to original owner of the territory if it’s liberated. No mention is made of returning the AA gun to its original owner.
Doesn’t that indicate that I get to keep the AA gun completely free of any strings tying it back to you? And wouldn’t that include technology?