there is a truck and leading into that truck there is a ramp of loose boards. there is a mine so be careful
grab and take the boards around the the front of the truck and prop one against the grill and climb up it. one atop the truck grab the board and place it as a bridge across the truck cabin to the back of the truck. good.
now go get more of the boards and bring them up here with you. this will take practice and patience but i have done it several times. keep saving as you go as the boards are fickle and easily fall back down. once you have all of the boards up here take them to the back of the truck and stack two of them on the back leftmost corner.
here is the first of two tricky parts. make a kind of triangular shape jutting out from the truck as far out as you can get the boards. as you are successful save frequently as you will have to drop the boards a few times to get them to stick out as far as they can go. good
now take the remaining boards and lay them across the truck half of the two that are sticking out to help weigh them down.
once you have this 'extension' to the truck you can run and jump off the ends of the boards toward the rooftop. you wont make it in your first leap so save first and keep trying. after three tries my initial attempt just when I had given this all up as impossible i made it and took a step forward and plummeted inside the building where i wasn't sopposed to be. you can find the outer door of the navy office and exit or load again. this time stay on the edge of the rooftop. there are plenty more solid segments of rooftop the walk on further along and you can even get all the way around to the front of the building. from up here there are some dogs and things to snipe at but really it is pointless.
do it just to say you pulled it off. I wonder if I alone discovered this or if anyone else had done it...