unsc would pwn. You can destroy a scorpion with a pistol, etc, cause it wouldn't be fair if to kill a scorpion you needed to fire like, two rockets or so. In real life, ceramic armour stuff and everything UNSC would pwn. I mean, the UNSC would just check what the government was like back then in their files, destroy all their nukes and bases that they learnt from these files, and kill them. Why would they be fighting their past selves anyway?  

Let me make it clear.

u.s.: oh-no! we r being attacked by our future selves for some unknown reason! Let's launch a nuke!

UNSC: says here we had a nuke site over here.... let's blow it up.

u.s. how did they know? let's launch our other nukes! wait a minute, the UNSC already blew it up! how come their always one step ahead of us?

In any case, the UNSC could send some pelicans to space and come down, dropping some bombs. If the U.s. fired missiles, up goes the pelican and the missile burns up in the atmosphere or runs out of fuel.

Also, about the UNSC planes, the one in FALL of reach has a big chaingun and missiles.