My players are about to be ambushed by a highly organized, well-funded group of mercs. They will set up an ambush with lots of cover and various weapon types. This is all well and good, and things I know well enough to wing them. However, there's one aspect that is very hard for me to plan out properly: The Navigator. We have no equivalent in our own world, so real-life experience won't help me think like these mercs.
How would you set up such an ambush as a GM? The players consist of a Seneschal, Arch-Militant, Void Master and Navigator (all of them rank 4 at this point). I want to be fair, so no hidden snipers starting combat with a headshot from long range. I also don't want to punish the players for having certain abilities. In other words, I want the Navigator to use her destructive powers, but I don't want it to be too easy.
What would a merc company bring along to help them combat a Navigator while minimizing the risk to themselves? I have a few ideas, but they all have weak points to them. I plan to have someone with a heavy weapon lay down supressing fire to force the Navigator to run for cover instead of attacking, but since the Navigator has the highest willpower in the group, that might not work out so well. I'm thinking I might have someone throw a smoke grenade at the players, hiding the Navigator's eye while allowing the mercs to drop grenades and other area attacks at the smoke even if they can't see the characters inside it. I might have the mercs attack in pairs, with one hiding completely behind cover while the other is somewhat exposed and firing, then the next turn they swap places. That way the Navigator can't affect more than 50% of the mercs at any one time, regardless of angle, but the mercs sacrifice some of their firepower by keeping half their squad out of combat at any one time.
Is there some equipment that is tailor-made for these situations? These guys are well funded, so as long as the equipment isn't unique or near-unique, it should be okay. They probably won't have archaeotech or xenotech, but you never know.
Suggestions? I want this fight to be exciting and deadly without being frustrating or too easy.