War bonds are a type of government debt security that is sold to investors to finance military operations during wartime. They are typically sold at a discount to their face value, and mature at a specified date, at which time the investor receives the full face value of the bond.
War bonds have been used to finance wars for centuries, and have played a significant role in funding the efforts of the United States during both World War I and World War II. In the United States, war bonds were first issued during the Civil War, and have been sold in every major conflict since then.