The TA31RCO is an Advanced Combat Optical Gunsight (ACOG) designed for the M4 and M4A1 weapon system (14.5" barrel). It incorporates dual illumination technology using a combination of fiber optics and self-luminous tritium. This allows the aiming point to always be illuminated without the use of batteries. The tritium illuminates the aiming point in total darkness, and the fiber optic self-adjusts reticle brightness during daylight according to ambient light conditions. This allows the operator to keep both eyes open while engaging targets and maintaining maximum situational awareness. Designed to the exact specifications of the United States Marine Corps, the unique reticle pattern Mfg: Trijicon