As soon I hop in the helio with my 3 cpu teammates, we fly over the sea and went straight over the naval base and circle it around. It didn't work as the objective would finish.
What I did was according to trueachievements.com, http://www.trueachievements.com/view...ntid=49243#vch
-The last mission. Assaulting the naval base is a pointless waste of time. After destroying the AAA vehicles, grab a helicopter, fly straight towards the ocean, make a fairly big turn and approach the naval base from the sea. Fly over the naval base once and you should get the "Objective Completed"marker. Note that you must have at least one squad member alive for this to work. Kudos to Le Garnisher for finding that out.
It doesn't work for me or I am doing it wrong?
Never mind, got it. Need to close this thread.