What type of mortar rounds contain red or white phosphorus?

The correct answer is smoke mortar rounds, which are designed to create smoke screens for obscuring movement or marking targets. These mortar rounds utilize red or white phosphorus as part of their composition. When the round detonates, the phosphorus ignites and produces a thick, billowing smoke that can provide concealment on the battlefield and assist in tactical maneuvers.

Other types of mortar rounds, such as high-explosive (HE) rounds, are intended for explosive effects against enemy troops or fortifications but do not incorporate phosphorus for smoke creation. Electronic mortar rounds, which are used for precision targeting and fire control, do not relate to smoke production. Illumination (ILLUM) mortar rounds are designed to light up areas at night for visibility rather than to generate smoke. Therefore, the unique function of smoke mortar rounds utilizing phosphorus clearly identifies them as the correct response to the question.