lets get on the same page...this is not a ww2 SUB game, but the sub could have a place in the game,if we are talking about the very small limited range 1-5 man subs that were used in ww2 by many nations,they could be used anywhere a pt could.  such as the class submarine japanese sub(pearl harbor) or german seehund,both saw combat and would fit into the game to fill a role(port defence)
Type XXVII B 5 (Seehund) midget submarine 
Class overview 
Builders: Germaniawerft, Kiel 
Operators:  Kriegsmarine
 French Navy 
Built: 1944–1945 
In commission: 1944–1945 
Planned: 1,000 
Completed: 285 
Active: 138 
Lost: 35 
General characteristics 
Displacement: 17 long tons (17 t) submerged 
Length: 39 ft (12 m) 
Beam: 5 ft (1.5 m) 
Propulsion: 1 x 60 hp Büssing Diesel engine
25 hp AEG electric motor 
Speed: 7 kn (13 km/h; 8.1 mph) surfaced
3 kn (5.6 km/h; 3.5 mph) submerged 
Range: 270 nmi (500 km; 310 mi) at 7 kn (13 km/h; 8.1 mph) surfaced
63 nmi (117 km; 72 mi) at 4 kn (7.4 km/h; 4.6 mph) submerged 
Complement: 2 
Armament: 2 G7e torpedoes