Many attempts to mount cannon on aircraft have been made, but owing to the recoil, the room necessary for mounting and manipulating, and the speed with which the gunner and the target move through the air, not much success was attained. Captain Georges Guynemer, the first great French flier to down more than fifty Hun planes, is credited with mounting a one-pounder on his Nieuport, single-seater. It could not shoot through the propeller, so it was arranged to shoot through the hub. The gun was built into the crank-case, the barrel protruding two inches beyond the hub. It is said that Guynemer brought down his forty-ninth, fiftieth, fifty-first, and fifty-second victims with this type of gun; but because of the fifty pounds extra weight above that of the machine-gun it was an impediment. Attempts to use on aeroplanes the Davis non-recoil gun, invented by Commander Davis of the United States navy, have not been entirely successful. The two-pounder is 10 feet long, weighs 75 pounds, and shoots 1.575 shell with a velocity of 1,200 feet a second. The 3-inch Davis fires a 12-pound shell and weighs 130 pounds. Several other guns have been used, and with the increase in the size of planes there ought to be much increase in the size of aeroplane guns. CHAPTER VII DEVELOPMENT OF THE LIBERTY AND OTHER MOTORS DEBATE IN REGARD TO ORIGIN OF LIBERTY MOTOR—LIBERTY-ENGINE CONFERENCE, DESIGN, AND TEST—MAKERS OF PARTS—HISPANO-SUIZA MOTOR—ROLLS-ROYCE—OTHER MOTORS There has been more discussion of the Liberty motor than any other motor made during the war. This was due to the publicity given to the motor by the publication of a romantic story of the motor, issued from Washington over the signature of Secretary of War Baker, to the effect that the motor was conceived in a few days, and built and perfected within a month. Of course every engineer knows that that could not be done, and it took at least six months before the Liberty engine was perfected, and this was long after the Creel Publicity Bureau in Washington issued its statement.