 On May 3 McClellan re @-@ entered federal service as commander of the Department of the Ohio , responsible for the defense of the states of Ohio , Indiana , Illinois , and , later , western Pennsylvania , western Virginia , and Missouri . On May 14 , he was commissioned a major general in the regular army . At age 34 , he outranked everyone in the Army other than Lt. Gen. Winfield Scott , the general @-@ in @-@ chief . McClellan 's rapid promotion was partly due to his acquaintance with Salmon P. Chase , Treasury Secretary and former Ohio governor and senator . 
