Jump signed up to serve during World War I, enlisting on December 22, 1917. He finished his studies at the University of California, Berkeley's School of Military Aeronautics, graduating on July 8, 1918, and proceeded to train for the war effort. He was among the first flight class to train at March Air Reserve Base in Riverside, California. Jump was prepared to serve as an Army Air Corps pilot, having received his Reserve Military Aviator rating, but the war ended before he was able to engage in any dogfights against Germany. On November 2, 1918, days before the armistice, he had been made a Second Lieutenant. He was able, however, to fly over Los Angeles for a war bond drive in 1918, along with classmate and future aviation pioneer Walter Varney. Afterwards, Jump spent two months as an instructor at the base, before being discharged on January 4, 1919.
