Unseen intruder

The first active camouflage you find can be used to get deep into enemy territory in the cavern. Before you use it, kill the Hunters and open the door. The moment you use the device, get into the Warthog or a Ghost and speed through the tunnel. If you get out just before the patrolling Elites, they won't see you, and you should have at least enough time to run across the bridge and start doing your worst. Plasma grenade, anyone? There's actually just enough time to open the far door and avoid a fight; but what's the point of that? You're not really going to let all those nasty aliens continue breathing are you?

If you've got a stolen Banshee you could instead fly in, and dismount somewhere to cause a bit of havoc while still invisible. E.g. you could land on the far platform and do some nasty deeds to those Elites and Hunters.