I will try to improve it when I got more time. There are two underwater bases which spawn units automatically, so your units probably destroyed the enemy underwater base. I could show the HP percentages in the multiboard to make it clearer.
I am also not really happy with the camera and targeting. Something from underwater might attack you while swimming, so you have to look underwater and check the level. I am not sure how to improve it. I could add the level with floating text to the units under water and maybe somehow list which units from which levels are attacking you or when torpedoes are following you. I don't want to make the water transparent since it should be part of the gameplay to have two different world one over the water and one under which can interact with each other.
There is a Z limit of 10 000. I have changed the fog Z to 10 000 as well in my development version on GitHub which removes the black borders but stuff will still appear/disappear. To fix that I will have either to change the angle of attack, so you cannot see everything in the distance or make the map rather small.
To fix changing the heights when under water there is a cliff I need to manually set the Z values or make some system which scans the heights under the water. I can only think of some system in which a dummy attacks the unit on the water and I measure the time the attack takes. There is no function to get the actual Z value under water. All functions return the Z value of the water surface.
Moving the mouse was intentionally left in since you might want to sell items from the inventory etc. but I think you are slower than using arrow keys. I might readd some Warcraft camera with a higher distance.
There is a hero icon for free camera view but if you deselect it, the camera will be reset. You can use the camera hero icon to look around your submarine. I want to change it, so your settings are kept and you can change the angle and distance a bit.
The different water depths and levels are part of the gameplay but I could reduce distance units and only allow you to attack units at your current level and only be attacked from units at your current level. This might avoid confusion, however I like the idea of being attacked on the water from some shooting creature under you. The whole map is a bit confusing because of the different units etc.
You cannot see what's going on under water but you have to protect your base under water etc. I am not sure how to improve this. I was also thinking about adding the ability to move to the left and right instead of rotating your view, so you can avoid torpedoes without auto target.