Fuck Ridge Island, fuck Grit, and fuck his "Hello my indirect fire units cover half the map and will kill anything that comes into range in one blow" units too. That War Room map is so insanely difficult compared to the rest of the maps in there. Every single advantage imaginable is given to Grit, with large amounts of cities (i.e income) natural chokepoints, and dense terrain, so approaching his artillery and rocket units is borderline impossible, while they'll kill anything that approaches instantly. The only feasible way I can imagine clearing that mission would be using Mech spam as Sami on the basis that he can't hit everyone at once, or going for some blatantly overpowered CO like Sturm.
Q: Artillery
A: Aircraft
That's true, but funny. I just double-checked, and Ridge Island doesn't have airports.
I think your best bet to beating it is Sami and APC cheese, Myroc. I don't think I ever beat it with a good ranking, though, if it is the map that I am thinking of.
Agreed on the infantry rush. Mechs are insanely powerful, surprisingly. I don't think a rocket can one-shot them on a forest or mountain, and they will quickly destroy indirect units in close-quarters. And you can field 5(?) of them per rocket launcher. If it's the map I'm thinking of, with a wall of mountains and forested chokepoints, then there's little to no chance of a tank ever getting into range... but infantry can swarm the hills, blot out the forests, and trade decently with the artillery.
...bugger, now I want to dig out my cartridge and see if it still works. Plus, check if I ever got a good rating on that map... I know I beat it, but I don't know if I got a passing grade.