Silent Service is a classic I remember well. The original version also works on the SM124 in ST-HIGH, I don't know if this is also true for the given Automation crack.
So we have a submarine simulation, and one of the earlier examples. You take command of a US submarine in the Pacific in WW2 hunting down japanese shipping.
The game plays in real time for the main sub view. Only patrol overviews are played on a map with time acceleration until enemy contact. The player can fire torpedoes and the deck gun with periscope and binocular view, a damage view and engine instrumentation is available.
Enemy ships can be quite pesky and I only managed once in a lot of tries to actually damage the carriers in the "Cavalla vs the War Fleet" scenario.
The game offers to play from a list of scenarios including target training aswell as going on patrol on various simulated dates. It helps to know your history book to actually find enemy shipping

Graphics are ok for 1986, sometimes a bit slow when large sprites are shown but functional and variied. Sound is a bit sad and not much better than beeper noise.
The gameplay is varying enough for some fun and there is quite a learning curve to master until you get to a satisfying patrol with 40000tons sunk

If you like submarines, this should be on your list to try. A very decent sim with a release date in 1986!
Note that the given menu for download seems not to be STE fixed....it flickers over here.