The Trijicon Acog 4x32 Dual Ill Red M855 Rco Ret is an Advanced Combat Optical Gunsight designed for the USMC M16A4 and M16M4 platforms, delivering precise 4x magnification with a 32mm objective and a durable forged aluminum housing. This TA31RCO-M855 integrates a dual illumination system that combines fiber optics and self-luminous tritium, ensuring the aiming point is always visible without batteries, with the tritium providing bright red illumination in total darkness and the fiber optic system adapting brightness in daylight for reliable reticle visibility. The horseshoe with dot reticle and Target Reference System is tuned to the 0.223 calibration for either 14.5 or 20 inch barrels, supporting quick target acquisition at close ranges while enhancing identification and hit probability to 1000 meters via the built-in Bullet Drop Compensator. External windage and elevation adjusters provide tool-free zeroing, and the optic remains waterproof to 11 meters without caps, contributing to field reliability in harsh environments. The package includes a TA51 mount, external adjuster assemblies and caps, a lanyard, a Scopecoat, a LENSPEN, a manual, and a warranty card, all designed to support operators seeking one-eyes-open operation, Bindon Aiming Concept, and consistent performance in daylight and low-light scenarios.