Go out of the building that you started at. Go up the hill outside, then go into the trench on your left until you reach a hill. Turn right, clear out the pillbox, then get out of the pillbox and go straight. Clear out the next pillbox. Go back out of the trench and turn to the right. There will be another trench here. Do not go into it yet. Pass it, turn right, and go downhill into another trench. There should be a path leading left as you enter the trench. Follow it and you will find the MG42, which is a machine gun that you can carry that is just like the stationary guns that were shooting you earlier.