A 400 h.p. Liberty supercharged engine was developed by Allison Engineering Company, using parts forged at Steel Improvement.

When the United States entered into World War I, The country had no real military aircraft. The Bolling Commission decided to produce proven European type aircraft in American plants. The one selected was the British de Havilland 4 (DH-4). Using Allison's Liberty engine, the DH-4 was renamed the "Liberty Plane" and placed in production at two Ohio plants, the Dayton-Wright Company and Fisher Body Division of General Motors.

	Another phase of DH-4 development was the standardization in 1919 of the DH-4b for use in the U.S. Post Office mail service Each had the capacity to carry 400 pounds of mail.
Liberty Plane de Havilland DH-4