MCRP 12-10B.1, page 204

d. Loopholes. A Marine may fire through a hole torn in the wall and avoid windows (Figure A-54). He/She stays well back from the loophole so the muzzle of the weapon does not protrude beyond the wall and the muzzle flash is concealed. Figure A-54. Firing From a Loophole e. Roof. The peak of a roof provides a vantage point for snipers that increases their field of vision and the ranges at which they can engage targets (Figure A-55). A chimney, a smokestack, or any other object protruding from the roof of a building can reduce the size of the exposed target and should be used. Figure A-55. Firing From the Peak of a Roof f. No Position Available. When a Marine is subjected to enemy fire and none of the positions mentioned are available, he/she should try to expose as little of himself/ herself as possible. When a Marine is in an open area between buildings (a street or alley) with no cover available and he/she is fired upon by an enemy from one of the buildings to his/ Military Operations on Urbanized Terrain A - 43