In 1917 the U.S. government issued Liberty Bonds to raise money for its involvement in WWI. After the war, these bonds were sold as Baby bonds. In the summer of 1940, with Fascist gains in the European war, discrete preparations for possible U.S. involvement in the war were begun.
The US Treasury began marketing the previously successful baby bonds as Series E defense bonds. After the Japanese attack on Pearl Harbor on December 7, 1941, their name was changed to War Bonds.