During World War II, she carried President Franklin D. Roosevelt across the Atlantic to Mers El Kébir, Algeria, en route to a conference of vital importance in 1943 in Tehran with Prime Minister Winston Churchill of the United Kingdom and Joseph Stalin, leader of the Soviet Union. When transferred to the Pacific Fleet in 1944, "Iowa" shelled beachheads at Kwajalein and Eniwetok in advance of Allied amphibious landings and screened aircraft carriers operating in the Marshall Islands. She also served as the Third Fleet flagship, flying Admiral William F. Halsey's flag at the Japanese surrender in Tokyo Bay.