This is the only Spec Ops Mission info I've seen so far.
In the Spec Ops Invisible Threat mode you can choose to wear the Juggernaut suit and you have to try to disarm IEDs (Improvised ExplosiveDevices), while your teammate is a sniper high on a roof.
EDIT: Even better source: http://www.blackwaterops.net/forums/showthread.php?t=21412
At first, I felt odd when I walked away from a hands-on co-op session of Call of Duty: Modern Warfare 3 earlier today at Gamescom. My colleague Alexander and I had just spent the past 20 minutes carefully defusing IEDs (Improvised Explosive Devices, for those of you who don't watch US broadcast news) and murdering potential assailants in a Berlin Spec Ops map, part of a mission named "Invisible Threat." Between laughs, furious button presses, and the occasional expletive, I realized we were having a lot of fun -- far more fun than two grizzled Battlefield vets expected to have with a Call of Duty title, anyway.
And soon after our play session, I understood why. That feeling I couldn't place was nostalgia, subtly reminding me that, yes, at one point I used to really enjoy Infinity Ward-developed shooters. As I carefully sniped oncoming baddies, Alex -- dressed in a "Juggernaut" bomb suit, a first for the series -- slowly lumbered around, dodging bullets/missiles/helicopters/tanks (seriously) while I assisted from above. Moreover, his ability to locate the remaining IEDs was based on me tossing up a UAV and spotting them from above, all the while dodging bullets/rockets myself. Of course, that meant I got to regularly drop missiles from said UAV onto the aforementioned waves of antagonists. Points!