I have ALWAYS wanted to do a hostage rescue film but have never been able to afford the highly specialist costume and props needed for my elite rescue team. Raider I am very jealous!
If you have to have an invisible enemy how bout a bunch of bad-ass Predator-type dudes who have kidnapped some important government advisor. Perhaps their ship has malfunctioned and the only guy to help them is this whiz scientist. ‘Coz their ship is so wasted they plan to take him with them in cast it breaks down again on their way back to their homeworld. (this bit need not be in the film but is explained as exposition in the briefing [see below])
The film could open with the elite rescue team; a proper bunch of bad-asses. Perhaps we could start with then being briefed in an APC (if you could use one; you are in the army, yeah?). This would be an easy way to explain the back story and set up the tone of the film. Lots of tension as they approach. Then a massive firefight as the aliens spring a trap on them. It would be important for lots of the good guys to get killed horribly by these shimmering aliens to show how scary they are. Lots of blood maybe?
The good guys realise that flash bangs (are they called that in the US?) temporally disable the aliens’ cloaks and make them a bit easier to see. The last couple of good guys left kill the last alien as he is about to self destruct the ship (also cloaked to ease the 3D workload). They rescue the scientist.
Its very cheesy I know, but I think it would be a huge amount of fun!
Sorry if I just went off on one there but I would LOVE to have access to all that kit and got a bit excited!!!
Whatever you decide to do; good luck with it!