The idea of driving and shooting at the same time is quite unique. What how chaotic would this be in multiplayer where different teams on different ships fight with each other. One sad suggestion is the way the water moves... it feels a little dizzy. Also try checking the Profiler in Godot to see what's eating up the load time, which should hopefully allow you to find the root cause of the lag spikes and fix it.
Overall it fits the theme, interesting mechanic.