The statement had been made that AA can fire at aircraft flying over them. Which is true if the AA is on land. But if that AA gun is at sea on a TRN, then the AF can fly right over it and ignore the TRN, the AA, and anything else below them on the seas.
… this fact is clarified on page 30 of the Operations Manual, in the Transports section. “Land units on a transport are cargo; they cannot attack or defend while at sea.”