Experienced SH3 player, but new to SH4...

I'd notices there were a lot of differences between the two games, but a few kind of stump me.

For example: Where's the detailed data on the sub types? If I'm offered an "upgrade", should I take it? What's this new sub do for me that the old one didn't? (granted, the upgrade offer doesn't actually tell me what the new sub will be, so that may be a bit moot... but I'd still like to be able to look it up afterwards. In SHIII I could comparison shop, but perhaps not in SHIV...)


Also... what are the substantial differences between the torpedo types? I see I can buy a Mk 23 torp for 100 renown... but all I get for it is the inability to get a longer range at a lower speed, or so it seems. Why would I want to buy this torpedo? (I can look up the canon torpedo types in Wiki (although I shouldn't *have* to), so I clearly want the Mk 14 ofver the Mk 10... but what's this Mk 23?)

Any assistance on this matter would be greatly appreciated. TIA!