:-D
Subs rule!
Just wish I could afford to buy more for Germany.
  I playtested a strat in the on-line gaming on the TripleA site where I defended Western Europe and bought an IC there on G2. The whole purpose of the IC in western Europe was to place subs in the 3 adjacent sea zones as needed! Specifically to keep UK from loading up troops and going into the Baltic to invade. It also played havoc in the western Med for allied shipping there as well.
Really competant allied players, with a great amount of patience usually overcame this expensive defensive strat. But others were so frustrated by it, that they usually capitulated by turn 7 or 8.  :-D