There were a lot of ships used in WW2, but let's just take 2 of my favorites:
Iowa-class battleship
| Installed power | 8 × water-tube boilers 212,000 shp (158,000 kW) |
| Propulsion | 4 × screws; 4 × geared steam turbines |
| Speed | 33 knots (61.1 km/h; 38.0 mph) (up to 35.2 knots (65.2 km/h; 40.5 mph) at light load) |
| Range | 14,890 nmi (27,580 km; 17,140 mi) at 15 knots (28 km/h; 17 mph) |
Gato-class submarine
| Speed | 21 knots (24 mph) surfaced 9 knots (10 mph) submerged |
| Range | 11,000 nautical miles (13,000 mi) surfaced at 10 knots (12 mph) |
| Endurance | 48 hours at 2 knots (2.3 mph) submerged 75 days on patrol |
| Test depth | 300 ft (90 m) |
Subs had to rely on ambush tactics. They were significantly slower than warships. They were able to keep up with some transports, when running at full speed using their diesel engines on the surface. A submerged sub running on battery power was quite slow. These are not today's SSBN's with nuclear reactors pumping power to their propeller blades 
In terms of communication, a sub could go snoop around an enemy shore, then sail away and make a radio report. But during battle, a sub had to be submerged, it could not coordinate with other warships in real time. That's why I think they should not be able to stack or move together. Unlike say a transport carrying disassembled planes, there's no different between that and a transport carrying infantry or guns. They got those backwards.
Subs also came in different sizes, anywhere from small coastal patrol vessels that returned to port every day to large, ocean crossing fleet subs that could stay out for weeks at a time. The game treats all subs the same, but gives us lots of different armored vehicles and types of planes. There are lots of opportunities to make subs more interesting and more realistic.