When Senator Ernest Lundeen, an isolationist, was killed in a plane crash, Stassen appointed Ball to fill the remaining two years of Lundeen's term. One of the youngest persons ever to become a U.S. senator, Ball, at thirty-five, was also the first senator to be required to register for conscription. After being sworn in on October 14, 1940, Ball stunned isolationist Republicans in his first speech on the Senate floor, calling for the United States to aid Britain as "a barrier between us and whatever designs Hitler and his allies may have on this continent".