Two Player Matches
Hope you didn't jump here without reading "One Player" first. The differences are really pretty minor and intuitive. The biggest difference is that, on the startup screen, there is now the option of having the sub's depth set manually by the opponent. If this is selected, a window for this purpose will appear at the beginning of each round. If the entered value is out-of-range, the opponent will be politely chided by the computer, which will proceed to establish a random depth for that round only.