MCRP 12-10B.1, page 78

Figure 3-3A. Towns and Cities Figure 3-3B. Defense of a Town or City 4 Large Built-Up Areas. Large buildings that are close together may require more forces and smaller defensive sectors than natural open terrain. The density of buildings, rubble, and street patterns will dictate the frontage of the unit. (b) O: Observation and Fields of Fire. Attackers must generally advance by crossing streets and open areas between buildings where they are exposed to fires from concealed positions. 1 Weapons and Range. The defender must position weapons to obtain maximum effect and mutual support. FACs and FOs should be placed well above street level for increased observation. Fires and final protective fires should be preregistered on the most likely approaches. 2 Limited Visibility. The commander can expect the attacker to use periods of limited visibility to sustain or gain momentum. (See Appendix H for more detailed discussion.) The commander considers the following during periods of limited visibility: Unoccupied areas that can be observed and covered by fire during daylight may have to be occupied or patrolled at night. Remote sensors should be emplaced in dead space. Mines, noise-making devices, tanglefoot, and OPs should be positioned on avenues of approach to provide early warning. Artificial illumination to include street lamps, stadium lights, and flares should be integrated into the overall defense. When defenses are probed, indirect-fire weapons, grenade launchers, and hand grenades can be used to avoid disclosure of defensive position locations. (c) C: Cover and Concealment. Although walls, floors, and ceilings can be used as protective cover, Marines should always improve these positions by using sandbags, rubble, etc. A defender can reduce his/her exposure by establishing routes between positions using: prepared breaches through buildings Military Operations on Urbanized Terrain 3-7