 On his return to Temple he went into partnership with J Walter Payne in the firm Roop and Payne.In June 1917 Roop enlisted in the army and was Chief Mechanic in the Truck Train of the Motor Transport Corp, rising to the position of Commanding Officer of the 15th Division's Truck Train based at San Antonio, Houston, and the Mexican border.He returned to the repair shop partnership with Payne in February 1919.