The great thing about modern versions of Axis and Allies, is that there is no one “simple” way to win every single game on a certain side.
Now mixed armies, combined arms, and mobility focus, are what rule the day.
Subs are another tool in the box, To be used according to ones need, They have their very special place.
Take a look at this current game vs DM
http://www.axisandallies.org/forums/index.php?topic=13870.195
This is how the odd sub or two, and good management of local starting pieces and Aircraft, can Keep Japan at bay, while still focusing on the European Campaign.