The mission where you walk the giant missile truck and you have to destroy the carrier (or something like that) at the end of the bridge. So far i think you go downstairs and then thats when i get stuck
there are two bomb areas that you need to activate. one is at the bottom of tower D and the other ate tower B. there are a couple of auto guns that you will naad to take care of. I sniped one whil standing by the car before I got to the bridge. after you activate them just head topside.
I have a post already made for people who need help. But thejarochs is correct, just head downstairs and take out the automatic guns one by one, then walk across the underside of the bridge to the other side, where Section D will be, and right by the door will be where you can interact (Press square) with a bomb.