I absolutely need to sing the praises of this game. I played the original version of this back when all you typically had on a home computer was 64k (and I do mean k) of memory. The entire western Pacific was your patrol zone. As you moved closer to shore, the detail of the shoreline would improve and you had to deal with shallower water. You had thermal layers (which hindered enemy sonar) to hide under.

If you played in the earlier years of the war, your torpedoes had a range of 4300 yards versus 3000 yards later in the war. This is because the earlier torpedoes were steam powered and the later ones were battery powered. But the trade off from the greater range was that the steam would leave a trail of bubbles on the surface of the water showing where the torpedo originated. There were two other problems with those earlier torpedoes. First, some of them would have water leak into them and would sink just enough to pass underneath the ship you were targeting. Second, the firing pin would sometimes shatter on impact and the torpedo wouldn't detonate. All of this technical history was incorporated into the game!

If you were not in the correct position to get in firing range of a convoy, you would have to move far enough away so that you could surface without being spotted and then do a speed run to get in position for an attack assuming the convoy didn't deviate too much from what appeared to be its course. (Back then submarines were faster on the surface than underwater. Plus the time they could remain submerged was limited.)

And one time, I had taken on so much water from damage due to depth charges that I was sinking rapidly. I had to blow all ballast tanks and that still wasn't enough to stop my descent. I had to go to full speed to get lift from the dive planes. And that gave the damage control enough time to stop the leaks and pump out all the water that had been taken on.

It just goes to show what programmers back then could do even with very limited resources.