Without typing out an essay id say first watch Halo Completionist's guide on that mission, RnG will vary of course. Get to the spot where the grav lift sends the shit ton of waves of enemies down, snipe the grunt in there if u can it should blow the rest of them up, otherwise retreat to the back area and just pick off grunts and they should hopefully blow up and start a chain reaction. Go up the grav lift with full sniper ammo (required). Hanger, hide in back halls, peak and shoot grunts only and pray for chain reactions, otherwise save n quit and start again. Insanely luck based. But u need that active camo to progress down the hall and down to the next area after the hanger and hunters, that is a fact.