40mm M585 Star Cluster Grenade

Overview: The M585 Star Cluster Grenade is a 40mm pyrotechnic signalling round designed for use with under-barrel grenade launchers (UBGLs) such as the M203, M320, and similar platforms. It is used for battlefield signalling, target marking, and illumination, deploying multiple bright-burning white star flares that rise into the air upon launch.

Development & Background: The M585 was developed to provide infantry units with a reliable and highly visible signalling device for use in low-light or night operations. Upon launch, the grenade ejects five to seven white star flares, which ascend to an altitude of approximately 200–250 meters before igniting and descending slowly. The bright flares ensure maximum visibility over a wide area, making the M585 a valuable tool for coordination, signalling, and emergency communication.

Service & Usage: The M585 Star Cluster Grenade is widely used for battlefield signalling, target marking for air support, and friendly unit identification. The white star cluster is commonly used as a general-purpose signal, often meaning rally point or attention marker in standard military procedures. The grenade is also used for distress signaling and visual communication between units operating in dispersed formations. The M585 is part of a series of star cluster grenades, with variants such as the M663 (Green) and M664 (Red) providing additional color-coded options for mission-specific signalling.