The Dual-Illuminated RMR uses fiber optics and tritium to illuminate the reticle. Fiber optics collect ambient light, automatically adjusting the reticle brightness. In situations with no (or low) light, the tritium illuminates the reticle. This version is popular with shooters who prefer a battery-free solution. The U.S. Marine Corps chose the 9.0 MOA dot for use in both the SDO and MDO optics programs.