1st Missouri , US Reserve Corps Infantry ( 3 months , 1861 ) The 1st United States Reserve Corps ( U . S . R . C . ) Infantry evolved from one of several unofficial pro - Unionist militia units formed semi - secretly in St . Louis in the early months of 1861 by Congressman Francis Preston Blair , Jr . and other Unionist activists . The organization that would become the First U . S . R . C was largely composed of ethnic Germans , who were generally opposed to slavery and strongly supportive of the Unionist cause . Although initially without any official standing , beginning on April 22 , 1861 the Unionist regiments Blair helped organize were sworn into Federal service at the St . Louis Arsenal by Captain John Schofield acting on the authority of President Lincoln . The first four regiments were considered to be the regiments of Missouri Volunteers called for under President Lincoln ' s April 15 , 1861 call for 75 , 000 volunteers . So many St . Louis Unionists mustered to volunteer , that after consultation with General - in - Chief Winfield Scott , and Secretary of War Simon Cameron , President Lincoln directed Captain Nathaniel Lyon to " enroll in the military service of the United States the loyal citizens of Saint Louis and vicinity , not exceeding with those heretofore enlisted , ten thousand in number , for the purpose of maintaining the authority of the United States ; [ and ] for the protection of the peaceable inhabitants of Missouri . " These additional regiments , in excess of the original Presidential call were designated " United States Reserve Corps " units , and were intended for local service . The First U . S . R . C . Infantry was mustered into service on May 7 , 1861 under Colonel Henry Almstead . Composed of men from St . Louis ' First Ward , the regiment was unusually large , with 1 , 200 men in 12 companies . The new Missouri Volunteer regiments , subsequently elected ( then ) Captain Nathaniel Lyon as the brigadier general of the new brigade of Missouri volunteers . President Lincoln would later confirm Lyon ' s promotion from Captain to Brigadier general . Military Service . On May 10 , 1861 the First U . S . R . C under Colonel Almstead participated in the arrest of the Missouri Volunteer Militia drilling at Camp Jackson at Lindell Grove on the western border of St . Louis City . As the Missouri militiamen were being march under guard back to the Arsenal near the riverfront , angry crowds confronted the Federal forces and the confused situation soon devolved into rioting and gunfire . Over 27 people were killed and the Camp Jackson Affair helped to polarize the state and send Missouri down the road to its own internal civil war . On May 18 , the regiment received an organic cavalry company , also raised from the First Ward " which did valuable scouting service " . The 1st U . S . R . C . carried out Provost duties in St . Louis , until June 20 , when the regiment conducted an expedition to Jefferson City ( June 20 – 24 ) . On duty in St . Louis from June 25 - July 29 . On July 29 – 30 , Cos " B " , " C " , " D " , " E " , " G " , " H " , " K " , " M " and Cavalry Co " A " marched to reinforce the strategic outpost at Bird ' s Point , Missouri , directly across from the Federal stronghold at Cairo , Illinois . This detachment remained on duty there until August 13 , when it returned to St . Louis . Meanwhile , a separate detachment composed of Cos " A " , " F " , and " L " had departed St . Louis , marching to Rolla , Missouri , and then to Cuba , Missouri , arriving there on August 10 . The three company detachment remained there until August 13 . The regiment ' s term of service expired on August 20 and the men were mustered out . Members of the regiment who wished to continue serving were reorganized as the 1st United States Reserve Corps Infantry ( Three Years Service ) , under Colonel Robert J . Rombaur , who had been the regiment ' s original Lieutenant Colonel . Casualties . Regiment lost during service 1 Officer and 3 Enlisted men killed and mortally wounded and 4 Officers and 25 Enlisted men by disease . Total 33 .