Vaughn learned to fly while attending Princeton University in 1917. He completed his flight training in England and was assigned to 84 Squadron as an S.E.5a pilot in May of 1918. Before his transfer to the United States Air Service on August 27, he had scored 7 victories while serving with the Royal Air Force. Vaughn scored his first two victories with the 17th Pursuit Squadron on September 22, 1918. Twice that day, he engaged Fokker D.VIIs, shooting down Friedrich Noltenius of Jasta 27 and Karl Bauerbfeind of Jasta 34 before his own Sopwith Camel was shot down by Wilhelm Neuenhofen of Jasta 27. Vaughn scored 4 more victories by the end of the war.

Distinguished Flying Cross (DFC)
"For conspicuous bravery in attacking enemy aircraft. On August 23, 1918, while on offensive patrol, he attacked an enemy kite balloon near Ham. Closing to almost point blank range, he fired upon it so that it burst into flames and was destroyed. Shortly afterwards, he observed an enemy two-seater near Maricourt. He attacked it, shooting it down from a height of 500 feet so that it was completely crashed. On August 22, he drove to its destruction, an enemy two-seater near Villers Carbonnel. In all, he has accounted for six enemy aircraft, five machines destroyed and one driven down dompletely out of control, and on kite balloon." DFC citation

Distinguished Service Cross (DSC)
"For extraordinary heroism in action near Cambrai, France, September 22, 1918. Lt. Vaughn, while leading an offensive flight patrol, sighted eighteen enemy Fokkers about to attack a group of five Allied planes flying at low level. Although outnumbered nearly five to one, he attacked the enemy group, personally shot down two enemy planes, the remaining three planes of his group shooting down two more. His courage and daring enabled the group of Allied planes to escape. Again on September 28, 1918, he alone attacked an enemy advance plane, which was supported by seven Fokkers, and shot the advance plane down in flames." DSC citation