Anti-Aircraft suggestion

My suggestion for the anti-aircraft is to give them the ability to be used on transport ships as a defense against planes. But to make sure it doesn't replace the destroyer as a defending class they could the transports defense +1. This will insure that if a plane attacks the anti air will raise its defense by 8 and be attacked before the transport. But if a destroyer attacks the anti aircraft wont get a defense boost and the transport will be attacked 1st, sunked, and taking the anti aircraft with it... without their intervention. Please give me some feed back if this idea would be OP or not, also if it is possible to do this without changing to many units in the process.

Wrong forum. Topic moved.

It would be very OP. Air units are your best bet against transports coming in seeing as how destroyers are expensive.