Hello. I have an interesting game idea I want to try out. I want to create a simplified real time 'ww2 u-boat' strategy. Not an 'u-boat simulator'  like Silent hunter, but a naval strategy - smth like naval battles in Total war (top view, several controlled ships, real time with pause/accelerate). I searched through existing games - 'Battle Fleet 2' looks similar to my idea (but it's turn-based, graphics too simple and controls are awkward). What I need is an engine with beautiful water graphics (cause it's almost everything you see on the screen). 'Water world', several simple ship models and lots of Ai programming is all I need to test the concept. 

I do believe I can realize my idea using complicated 'Arma' engine for example (It's heavy, it's full 3D, and i have some experience with it - but it's possible to create a game out of it, only game MOD) 

What would you recommend? Unity, CryEngine ? 

Unreal engine 4. It is totally free, including shader support, since shaders are needed to create life like water visual effects. Unity has shaders but it is the paid option.