Makes sense, CB, but I'd still leave at least two infantry in W. Europe on G1 or G2. That way England MIGHT get one with their battleship, but would still need to risk 7 IPCs to get the other one (or more.) I'd probably leave the AA Gun there too, just to encourage England to avoid bringing Fighters, but I might not depending on how well I'm doing.
Also, do note that my comment above about British destroyers to out-think the German fleets that later pull their fighters back can be out thought by Germany just by producing a submarine in SZ 5 each round.
I'd say the submarine is a good investment when, and if, England gets 5 destroyers and their starting Battleship. Anything less than that and you may not recover your investment on the submarine. (5 Destroyers = 15 Punch, 1 Battleship = 4 Punch, that's 19 punch or roughly 3 hits. 3 hits = 9 IPC in infantry, a submarine costs 8. Therefore, the submarine is cheaper than the lost infantry.)