From new A&A Europe Rule Book, reprint and purchased this week.
Page 30, last paragraph under Air Units: Air units can hit submarines only if a friendly destroyer is in the battle.
Page 32, Submarines: Unit Characteristics: Can’t Be Hit by Air Units: When attacking or defending, hits scored by air units can’t be assigned to submarines unless there is a destroyer that is friendly to the air units in the battle.
Page 32, Destroyers: Unit Characteristics: last paragraph … cancels the following characteristics of all enemy submarines in that battle: Surprise Strike, Submersible, and Can’t Be Hit by Air Units. …