An early opponent of American involvement in World War II, Shriver was a founding member of the America First Committee, an organization started in 1940 by a group of Yale Law School students, also including future President Gerald Ford and future Supreme Court Justice Potter Stewart, which tried to keep the US out of the European war. Nevertheless, Shriver volunteered for the US Navy before the attack on Pearl Harbor and said he had a duty to serve his country even if he disagreed with its policies. He spent five years on active duty, mostly in the South Pacific, serving aboard the , reaching the rank of lieutenant commander (O-4). He was awarded a Purple Heart for wounds he received during the bombardment of Guadalcanal.