Yeah, what they said.
Plus, ships, ships, and more ships, early in the game. Love to see those arrogant cruisers head for the bottom.
For cargo ships, cannons into the engine/bridge area, followed by a rocket or two. Using P38J/L, you can get 5 a mission if you are lucky, plus what your wingmen bag. This seems to help keep the Germans low on supplies and slow down invasion attempts.