We ran some sims this last week regarding this, and as YG pointed out, the subs are easy to ignore until they are on your convoys and it takes forever to get them there. The ironic result is that we found a couple of ways of hiding/protecting JAPANESE subs and ships by spreading them out and only placing them where Destroyers didn’t want to be, but there was not much of a intimidation factor created by having the subs spread out among carolines, Hawaii, queensland, or anywhere else in between.
Some of the respondents talked about getting a massive stack of subs, complementing it with a few carriers so that you have 2-4, ignoring BBs and just taking the surface ships that you get at the beginning of the game along. America doesn’t really want to ‘dance’ around with Japan in the northern pacific because they can never achieve odds; the SS strategy may well be very intimidating to SZ 6 and force the Japanese to garrison it in great force. Unf. you need to do this before Japan reaches peak income or he will be able to buy up enough defense to stop your invasion.
The interesting dynamic there is that as soon as the last Japanese destroyer is killed, their planes can no longer hit the subs. The destroyers are prime causalities because of their low cost, so are the subs. But if you can land 6 sub hits from 20 subs, and they still have to retain a destroyer or lose the ability to hit your subs…then they have to make some bad choices about what to lose. since they can still slaughter your surface ships, it could result in a battle where American subs survive but neither Japanese nor American fleets do…then its just planes v subs…until japan brings up one more DD and wipes you out.