Which round would be used for training purposes?

The M879 round is specifically designed for training purposes. This round simulates the performance characteristics of a standard mortar round but is manufactured with a lower-cost and less hazardous payload, making it ideal for training environments. Using M879 allows troops to practice firing techniques, aim adjustments, and familiarize themselves with mortar systems without the risks associated with live munitions.

In contrast, the M880 is typically a high-explosive round used in combat scenarios, the M889 is designed for illumination to help in battlefield visibility, and the M888 serves as a target practice round but is not the primary choice for general training. Each of these rounds serves different roles, and the M879 stands out as the go-to option for safely developing skills and ensuring proficiency during training exercises.