C-41. Illumination and obscuration missions are important functions for mortar platoons or sections. Atmospheric stability, wind velocity, and wind direction are the most important factors when planning target effects for obscurants and WP mortar rounds. The terrain in the target area also affects obscurants and WP rounds.
C-42. The bursting WP round provides a screening, incendiary, marking, and casualty-producing effect. It produces a localized, instantaneous obscurants cloud by scattering burning WP particles.
C-43. The WP round is used mainly to produce immediate, close point obscuration. It can be used to screen the enemy’s field of fire for short periods, which allows troops to maneuver against him. The 60-mm WP round is not sufficient to produce a long-lasting, wide-area obscurants screen, but the much larger WP round from the heavy mortar is.
C-44. WP rounds generally should not be used solely to produce casualties due to the law of war principle of unnecessary suffering. Unnecessary suffering would be implicated because of the persistent burning WP causes in the wounds it produces and the availability of a superior round for producing casualties, the HE round. While the bursting WP round can produce casualties among exposed enemy troops the casualty-producing radius of the WP round is much less than that of the HE round. Generally, more casualties can be produced by firing HE ammunition than by firing WP. A few WP rounds mixed into a fire mission of HE rounds for a valid purpose (that is target marking) may increase the suppressive effect of the fire because of the significant psychological effect a WP burst may have on exposed troops.
C-45. When WP is used for its incendiary and casualty-producing effects it should not be used against the civilian population, or civilian objects. The Law of Armed Conflict also prohibits the use of incendiary weapons against military objectives located in “concentrations of civilians,” unless the military objective is separated sufficiently from civilians and civilian objects to prevent collateral damage.
C-46. The WP rounds can be used to mark targets, especially for attack by aircraft. Base-ejecting obscurants rounds, such as the 81-mm M819 red phosphorous round, produce a dispersed obscurants cloud, normally too indistinct for marking targets.
C-47. The effects of atmospheric stability can determine whether mortar obscurants is effective at all or, if effective, how much ammunition will be needed:
- During unstable conditions, mortar obscurants and white phosphorous rounds are almost ineffective the obscurant does not spread but often climbs straight up and quickly dissipates.
- Under moderately unstable atmospheric conditions, base-ejecting obscurants’ rounds are more effective than bursting white phosphorous rounds. The M819 red phosphorous round of the M252 mortar screens for over 2 and a half minutes.
- Under stable conditions, both red phosphorous and white phosphorous rounds are effective.
- The higher the humidity, the better the screening effects of mortar rounds.
C-48. The M819 red phosphorous round loses up to 35 percent of its screening ability if the ground in the target area is covered with water or deep snow. During extremely cold and dry conditions over snow, up to four times the number of obscurant’s rounds than expected may be needed to create an adequate screen. The higher the wind velocity, the more bursting WP rounds are, and less effective burning obscurant’s rounds become.
C-49. If the terrain in the target area is swampy, rain-soaked, or snow-covered, then burning obscurant’s rounds may not be effective. These rounds produce obscurants by ejecting felt wedges soaked in red phosphorus. These wedges then burn on the ground, producing a dense, long-lasting cloud. If the wedges fall into mud, water, or snow, they can be extinguished. Shallow water can reduce the obscurants produced by these rounds by as much as 50 percent. Bursting WP rounds are affected little by the terrain in the target area, except deep snow and cold temperatures which can reduce the obscurants cloud by about 25 percent.
C-50. Although bursting WP rounds are not designed to cause casualties, the fragments of the shell casing and bits of burning WP can cause injuries. Burning obscurant rounds do not cause casualties and have little suppressive effect.
Next: C-51: Illumination