It is difficult to acknowledge fully the assistance given by persons and museums for the preparation of this book. However, I wish especially to thank Hugo T. Byttebier, engine historian, Buenos Aires, Argentina; Dipl. Ing. Hermann I. A. Dorner, diesel designer, Hanover, Germany; Harold E. Morehouse, and C. H. Wiegman, Lycoming Engines, Williamsport, Pennsylvania; Barry Tully, Goodyear Aircraft, Akron, Ohio; Richard S. Allen, aviation author, Round Lake, New York; William H. Cramer, brother of Parker D. Cramer, Wantagh, New York; Erik Hildes-Heim, Early Bird and aviation historian, Fairfield, Connecticut.

I am particularly grateful to curators of the following museums who have been so generous in their assistance: Deutsches Museum, Munich, Germany (Dipl. Ing. W. Jackle); Henry Ford Museum, Dearborn, Michigan (Leslie, R. Henry); U.S. Air Force Museum, Wright-Patterson Air Force Base, Dayton, Ohio (Maj. Robert L. Bryant, Jr., director); Science Museum, London, England (Lt. Comdr. (E) W. J. Tuck, Royal Navy). The preparation of this paper could not have been accomplished without the aid of the National Air Museum of the Smithsonian Institution and the help of Philip S. Hopkins, director, and Paul E. Garber, head curator and historian.