Barkhang Monestary Crate Puzzle

Pull the first crate to the left, then push it foward, then pull it toward the doorway so it covers it:

Pull the one behind it once, so it's in the place where the first one was:

Climb over it to pick up some automatic pistol clips.

Climb up and pull the crate on the left over crate #2:

Jump down and climb up to where the crate was to pick up some harpoons.