Thanks for the feedback. The game is complete, as far as js13kgames competition goes, so it should work. I only tried the game in Chrome on Mac. The deadline for the competition is today, so I will look into other browsers and operating systems trying to fix the issue you are facing.
If ships aren’t moving, try pressing «space» (if you haven’t already) to start the round. When there’s just one ship left, press «space» again to re-start the round.
The walls are actually just the border between the play area and the white space outside of it. I can add a border color to make it easier to see.