Thank you! I'm so glad you've enjoyed it. It was fun to make.
Theoretically, the save function is only available when you're inside the submarine (the top-down section) and press the start-button or "enter." It was a weird function to try and make work. Though, if you're playing the ROM version with an emulator, those frequently have a "save state" option that should do the trick.
That said, you can get through the game within about 10 to 15 minutes.
Thanks again for checking it out!