Choose the Rocketeer. Before you use a gun. press 3 then use it. You must press 3 every time you change the gun. Note: If this is done and you have not changed the gun you will not be able to zoom.
At the center of the map, find a rectangular metal "hill". Jump to the side to find the entrance. Once inside, you will enter an area with a black floor with boxes on each corner. Use those boxes to recharge your guns.
