Struggled to figure out the mechanic. Started by just playing. My first assumption was to try and create vertical rows of colours. In my mind this was the metaphor that you're clearing the path for the torpedo, so the more lined up things were the better it would travel. I then tried clumping colours together. Basically I went from connect four to match 3 mechanics. I re-read the symmetry instruction, but I couldn't figure out what the desired axis of symmetry was so I gave up and just tried the clumping strategy for a while.
I then tried spamming for a while and that's when I noticed that some torpedos actually miss. I then thought it would be nice to get some kind of info on how close I was to destroying the opposition. It was only at this point where I felt like I'd finished playing that I then ignored the clear an present danger of the other ship and tried to figure out the relationships between all the elements of the interface. This was the first time I actually "saw" any of these interface elements. This is interesting in that it shows you how effective humans are at filtering out information, especially when there is a clear and present danger.
So this was the first time I noticed the damage and accuracy bars. With this I started to build a model of the desired symmetry, but I still don't quite grok it. I also noticed that indeed there was a counter showing your oppositions health.
I did however really enjoy the feel of your main interaction. When I figured out how to use a six block area to move a tile to where I wanted it, that was a particularly nice moment. I enjoyed the sense of speed solving, and having to trade off how solved the puzzle was against just getting a new puzzle. I think there is something there and that the dressing around the game is completely incidental (eg its about the grid and not about smashing subs). This means that you could strip away the entire interface (I was ignoring anyway) and just have the grid. Would make for an interesting mobile game.
Also I think staring on a smaller grid with a target that doesn't fire at you would be a great way to gently introduce the concept. Also not regenerating health between rounds felt really punishing. ;)