This was hard to figure out but once I figured out what was going on, I was able to get up to day 3. I was feeling like I wasn't in any danger until day three when I got attacked. I used the button to lock and fire but I didn't know how it worked. I would have preferred having a heading (0-360 degrees) instead of an X,Y coordinate system. I got damaged to 40% and surfaced to 99m but I couldn't do anything else except to put torpedoes in the hole. I guess I died? I think you could have used more audio cues like creaking, locking, firing, etc.
Overall, a great entry!