OVERVIEW: The Mk 171 “ChaffStar” is a 112 mm rocket-assisted chaff round used in the U.S. Navy's Rapid Blooming Offboard Chaff (RBOC) system. It is designed to counter radar-guided threats by creating radar-reflective decoy clouds for seduction.

DETAILS: The Mk 171 is launched from 112 mm decoy launchers such as the Mk 36 SRBOC system, which uses fixed-angle mortar-style tubes to deploy chaff and infrared countermeasures. The round contains radar-reflective dipole material, typically aluminum-coated fibers, tuned to radar frequencies used by common missile seekers. Upon launch, the rocket propels the round to a safe distance from the vessel, after which it disperses its chaff payload in a rapidly expanding cloud. This cloud acts as a radar-reflective decoy, drawing enemy radar seekers away from the ship by simulating a larger radar cross-section.

FONCTION:
Launched from SRBOC 112 mm mortar tubes in response to radar threat detection.
Propelled away from the ship before releasing dipole chaff material.
Forms a false radar target to seduce and misdirect incoming missiles.

SOURCE:
Federation of American Scientists (https://man.fas.org/dod-101/sys/ship/weaps/mk36.htm) ; GlobalSecurity.org ; Wikipedia (https://en.wikipedia.org/wiki/Rapid_Blooming_Offboard_Chaff)