DeHavilland became a naturalized citizen of the United States on November 28, 1941, 10 days before the United States entered World War II militarily, alongside the Allied Forces. During the war years, she actively sought ways to express her patriotism and contribute to the war effort. In May 1942, she joined the Hollywood Victory Caravan, a three-week train tour of the country that raised money through the sale of war bonds. Later that year she began attending events at the Hollywood Canteen, meeting and dancing with the troops. In December 1943 deHavilland joined a USO tour that travelled throughout the United States and the South Pacific, visiting wounded soldiers in military hospitals. She earned the respect and admiration of the troops for visiting the isolated islands and battlefronts in the Pacific. She survived flights in damaged aircraft and a bout with viral pneumonia requiring several days' stay in one of the island barrack hospitals. She later remembered, "I loved doing the tours because it was a way I could serve my country and contribute to the war effort."