First, I am assuming that all submarines in A & A attack from periscope depth, not the surface. That is the only way that the first strike rule for submarines can be justified. If all subs are attacking on the surface then aircraft should be able to attack subs without a destroyer present, and all surface ships should get a free shot at the sub with no chance of reply, as most successful torpedo attacks occurred at ranges of less than 2,000 yards, point blank range for surface guns. The attack chance is based on a submerged sub attacking a sub running on the surface, not submerged. WW2 boats spent most of their time on the surface, submerging only to attack or avoid aircraft and surface ships. The snorkel only came into use by the Germans in mid-1944, and did allow for diesel running while submerged. If you wish, I will post a detailed discussion of WW2 submarine tactics and operational proceedures. If you argue that all subs are always submerged, then they should have a movement of 1 sea zone every two turns, to reflect the very low speed of submerged running. You cannot have it both ways.
OK yes submarines attacked at periscope depth and then immediately submerged at the first sign of trouble. And what the ‘first strike’ idea is supposed to model. However, fighters didn’t have the tactic of attacking subs down until the mid war period and up until that time reconnaissance planes ( in our case bombers) were used as spotters for convoy or for wolf packs to hunt convoy system. Those snorkel types you mentioned are the type XXI Walter U-boat turbine system which could travel in some cases underwater faster than some allied destroyers ( about 16 knots). Also you have to know that a turn in AA is something like 4-6 months which is plenty of time to move around and not really effect its movement. The 2 movement point thing is for play balance issues because if naval vessels had unlimited range it would mess up the game because its already a highly abstracted strategic system.
As for a submerged submarine sinking a submerged submarine, the HMS Venturer sank the U-864 while both were submerged on February 6, 1945. This is the first recorded case of a submerged sub being sunk by another submerged sub. Both the US and the UK in the immediate postwar period began the development of hunter-killer subs designed specifically for submerged ASW engagement. During WW2, British submarines sank 35 enemy submarines. I will need to check on the totals for the other countries.
I knew you would bring up that example: but the game is representing one submarine as something like 20-40 submarines for each ‘piece’ and that is only one example near the last days of the war. Hardly anything to base a major principle of naval combat on IMO. The game has to reflect what actually happened as a matter of normal affairs during the war . All postwar developments wont help us model WW2.