Question: what president brought us into world war 2

title: Military history of the United States during World War II
text: Another notable example was the Flying Tigers , created by Claire L. Chennault , a retired U.S. Army Air Corps officer working in the China since August 1937 , first as military aviation advisor to Generalissimo Chiang Kai - shek in the early months of the Sino - Japanese War . Officially known as the 1st American Volunteer Group ( AVG ) but nicknamed the `` Flying Tigers '' , this was a group of American Pilots already serving in the US Armed forces and recruited under presidential authority . As a unit they would serve in the Chinese Air Force to fight against the Japanese . The group comprised three fighter squadrons of around thirty aircraft each , the AVG 's first combat mission was on 20 December 1941 , twelve days after the Pearl Harbor attack . On 4 July 1942 the AVG was disbanded , it was replaced by the 23rd Fighter Group of the United States Army Air Forces , which was later absorbed into the U.S. Fourteenth Air Force . During their time in the Chinese Air Force , they succeeded in destroying 296 enemy aircraft , while losing only fourteen pilots in combat .