The improved white phosphorus (IWP) M994/5 smoke cartridge is used for target screening.
The cartridge produces dense white smoke instantaneously upon the target which persists for a longer period than smoke produced by the conventional munition. This cartridge also has a secondary incendiary effect.
This 120mm IWP smoke cartridge belongs to a new generation of enhanced long range mortar ammunition. It is type classified and suitable for firing from all 120mm smooth bore mortars.
This mortar cartridge includes a propulsion system containing four identical combustible water repellent propelling charge increments.
The cartridge body contains felt wedges arranged in layers and saturated with white phosphorus (WP).
A burster charge, located in a central cavity, runs the entire length of the body.

After the projectile is fired, it proceeds along its ballistic trajectory.
At a very low height (about 10 m) above the target (with proximity fuze) or on impact (with PD fuze), the fuze functions and activates the HE burster. The explosion ruptures the projectile body and disperses the WP saturated felt particles over the target area. The WP ignites spontaneously upon contact with the air and produces a dense and persistent white smoke.
The secondary incendiary effect of the WP filling has been considerably enhanced in this new cartridge, due to the dispersal of many particles of burning WP saturated felt over the target.