The premise is simple. I feel that the watercrafts in the minor factions are too bare-bones, especially in MFDM.
I'll admit that I don't know how much water, or even if there is any, on MFDM maps. But if its enough for naval combat then that part would be extremely boring, since at best the minor factions amphibious units and aircraft fight alongside their army of single vessels.
I'm not asking to put in enough naval units to rival the main factions. But maybe one or two more watercraft to make MFDM naval battle more exciting.
With that I have some personal suggestions:
GLA: A "submarine", made of a metal tube with a window and engine welded on it, that acts as a scout and/or anti-air sub. whose ability is to suicidally charge at their enemy and explode, like the Yari in vanilla red alert 3.
Blue China: A bombardment ship that uses the Silkworm Missile Pod
Vietcong: A ship or submarine that has an incredibly large cannon. Either disguising itself or staying submerge until they get in range and fire, its shot easily killing most vessels and structures but its range is short, before escaping retaliation
Unless of course MFDM was never meant to have naval combat. In that case nevermind.