Rubuta ci gaba don wannan sakin layi - An kunna Rundunar Sojan Ruwa ta 21 a ranar 14 ga Yuli, 1942, a Camp Elliot, San Diego, California, amma a zahiri an shirya shi a New River, North Carolina. Yawancin membobin farko na rundunar sun fito ne daga Rundunar Sojan Ruwa ta 6. An sanya su zuwa 3rd Marine Division, duk da haka daga Janairu zuwa Yuni 1943 sun kasance wani rukuni mai zaman kanta. A lokacin yakin, rundunar ta shiga cikin yakin Bougainville, yakin Guam (Fig. 1) da yakin Iwo Jima. Bayan da Japan ta mika wuya
, 21st Marines sun koma Guam inda aka kashe su a ranar 20 ga Disamba, 1945.