Ok when you start in Patriotic Defense  if you turn around (probably
after you kill the tank and they guys that come after it) you will see a
shut wooden door. when you come up to them lie down on one of the sides.
You will then go forward a little and aim upwards and start moving
backwards. If you do this correctly you will be able to move backwards
and run around and kill all the people. You might have to try a couple
times before you get it.