You have to have enough room to get out of vis range surface run ahead of it then submerge and engage.
but you need a large area to get ahead of one. by itself there is not much chance but if its slowed by escorts.... 
WW2 fleet boat could do 20ish knots surfaced. Most military ships could outrun them if need be. Submerged were looking more at 10ish knots depending on batteries charge. Currently, TG steam on flank all the time doing 30ish knots. No racing for position on the surface they simply are too fast.
About the OP : The introduction of submarine would need a lot more work than thought. We got to have a viable submarine model. Not a nerfed one like in say Battlestation or Enigma : rising tide. Introducing Sub also brings on the need for ASUW capable platform. In my opinion, the PT is not the best option for that as they were not sub hunters in the first place. We would also need much more flexible TG in that we need to be able to detach escort to engage submerged contact. The introduction of detection systems as the ASDIC and passive sonar and maybe even passive anti-sub defense network (IE : anti-sub net). Introduction of depth charge and plateform for them. Again PT would not be the best for this as they couldn't carry alot. And the most important point as many have already mentioned would be the introduction of a meaning for it. Also, These things are slower than their (current) targets. One could spend an evening setting up a shot only to be denied because someone turned the TG. Unlike games like Silent Hunter (in which you can accelerate time) , the world in AH evolve in real time so a chase that take 5 min in SH but 6 in-game
would take 6 hours in AH with no guarantee you'll ever get your mark. That would bore me to death. And I'm not really easily bored. Many are quicker than me to pull the plug.
If Subs are ever put into the game, they need to be FUN !
Exactly. I don't think they could without being nerfed up completely.
Can you imagine Sub dogfights? I can. 
They have to be steerable like the PT Boats.......and fast to dive.
Historically, they were not. See my comment about nerfing them up...
If the subs are boring, no one will ever use them.
Ataboy! Your right... in a MMO, they'll be despairingly slow and it'll make for long, boring patrols even if there is tons of things to shoot at. The time it take to cover distances is long. Steaming 20 knots surfaced, we're looking at over 1:15 hour to cross one square of the map. Unless all the water is completely riddled with boats, transit time fast becomes prohibitively long.
Will Subs be able to spawn camp? Why not.
Indeed, why not? If you camp TG spawn, ok. A PT spawn, not so. A PT is not a good target for torpedoes. Not enough draft, too small and too fast. You aim one of those at the center of a 200 feet long boat steaming at 10 knots and your lucky if it hits within 40 feet of your aimed point.
