Rubuta ci gaba ga wannan sakin layi - Gilbert ya shiga rundunar sa kai daga baya fiye da yawancin abokan zamaninsa, ya shiga cikin Oktoba 1862. Duk da haka, an nada shi a matsayin colonel na 27th Iowa Volunteer Infantry Regiment a ranar 3 ga Oktoba, 1862. Rundunar Gilbert ta shiga cikin Frederick Steele's Little Rock Expedition
amma bai shiga cikin wani fada ba. An aika shi zuwa aikin garrison a Arkansas sannan aka tura shi zuwa Mississippi inda aka sanya rundunarsa zuwa sashen Andrew J. Smith a cikin XVI Corps a lokacin da ake kira Meridian.