There are quite a few scenarios and levels of play to choose from, so this game should cater to almost everybody. First, you have the choice between 3 simulation options: "Torpedo/Gun Practice", "Convoy Actions", and "War Patrols". Then, you have to choose a skill level: MIDSHIPMAN (beginner), LIEUTENANT, COMMANDER (designed to be the most historically correct), and CAPTAIN (expert). After that, you need to make up your mind on the various combat difficulty levels (it's an on/off thing): limited visibility, convoy zigzags, dud torpedoes, port repairs only, expert destroyers, and convoy search.
Game play is smooth sailing until you have to deal with the destroyers. Those pests are gonna do everything they can to make your life miserable. Once a destroyer has spotted you, you better perform some quick evasive action or drop to the bottom of the sea. When the destroyer circles around your submarine (that you have wisely brought deep down) and the depth charges explode around you, I guess you kinda feel like you are in that epic movie "Das Boot". There's definitely much more in that simulation than just aiming at cargo ships, firing torpedoes, and getting the hell out of there. That's why it's called a simulation.
The boring parts can be alleviated by speeding up time (press F), up to 32 times faster than real time. When things need immediate attention, real time can be restored by pressing N.
In the video above, I play the "Wahoo vs. Convoy" scenario with the default (easy) settings. The fact that I can sink a kaibokan (escort vessel) with surface guns shows how unprotected that convoy really was or how easy the game settings I have chosen are. A real destroyer would have forced me to evade or go into hiding (I think).
To play this submarine simulation game, you'll definitely need to go over the Silent Service manual.