True aerial combat was made possible when Anthony Fokker designed a cam-operated interrupter gear, connected it to the oil-pump drive of an Oberursel engine and the trigger of a Parabellum machine gun, and synchronized the gun to fire through a moving airplane propeller.
The first true aerial combat of World War I began in 1915. Until that time, defensive and offensive weapons attached to airplanes were inadequate for any real combat work. Pilots and crew members used handheld weapons and clumsily mounted machine guns in attempts to convert their observation planes into fighters. In the spring of 1915, the German army had 230 frontline aircraft to the Allies’ 500. On April 1, 1915, this situation became even more lopsided. From an airfield near Dunkerque, France, a French airman, Lieutenant Roland Garros, was armed with a device that would make his plane the most feared weapon in the air at that time.
Prior to the war, Garros had been an acclaimed exhibition pilot, holding the world altitude record and becoming the first person to fly across the Mediterranean. As a combat pilot, however, Garros was frustrated by the inability to maneuver his aircraft into a position where either he or his observer could bring weapons to bear on the enemy. During a visit to Paris, Garros met with Raymond Saulnier, a French aircraft designer. In April of 1914, Saulnier had applied for a patent on a device that mechanically linked the trigger of a machine gun to a cam on an airplane engine shaft that, theoretically, would allow the machine gun to fire between the moving blades of the propeller. Unfortunately, the available machine gun Saulnier used to test fire his device was a Hotchkiss gun, which tended to fire at an uneven rate. The low-quality ammunition produced for the Hotchkiss gun resulted in a large number of delay-fired rounds. No device could prevent the Hotchkiss gun from mistiming and destroying the propeller.
On Garros’s arrival, Saulnier showed him a new invention: a steel deflector that, when fastened to the propeller, would deflect the small percentage of mistimed bullets that would otherwise destroy the blades. The first test firing was a disaster: The propeller was shot off and the fuselage was destroyed. Saulnier modified the deflector braces, streamlining the deflector into a wedge shape with channels for deflected bullets. The invention was attached to a Morane-Saulnier monoplane. On April 1, Garros took off alone in the plane toward the German lines. For the first time, a fast, maneuverable airplane—of a design suited for aerial combat—was armed so that the pilot could use the plane for aiming directly at a target.
Success was immediate. Garros shot down a German observation plane that morning. It was the first time a flier ever aimed an aircraft as a weapon and shot through the propeller to bring down an enemy. During the next two weeks, Garros shot down five more German aircraft. The German high command, frantic over the effectiveness of the French “secret weapon,” sent out spies to try to steal the secret and also set up armament committees to develop a similar weapon. As it turned out, luck was with them. On April 18, 1915, despite warnings from his superiors not to fly over enemy-held territory, Garros was behind German lines when engine trouble forced him to crash-land. Before he could destroy the aircraft, Garros was captured by German troops, and the secret weapon was revealed.
The Germans were ecstatic about the opportunity to examine the new French weapon. Unlike the French, the Germans had the first air-cooled machine gun, the Parabellum, which shot continuous bands of one hundred bullets and was reliable enough to be adapted to a timing mechanism. In May of 1915, the German high command sent a message to Anthony Fokker, who at that time was building airplanes for the German Signal Corps in Schwerin, and asked if he could produce a forward-firing machine-gun mount similar to the one used by the French. Fokker was shown Garros’s Morane plane and was ordered to copy the idea, but instead Fokker and his assistant designed a new firing system. The design was similar to an interrupter gear patented in 1913 by German designer Franz Schneider, who had devised a method of shooting through the air-screw shaft in the same year. Both these inventions had been overlooked by the military.
It is unclear whether Fokker and his team were already working on a synchronizer or to what extent they knew of Saulnier’s previous work in France and Schneider’s in Germany. Within several days, however, they had constructed a working prototype and attached it to a Fokker Eindecker 1 airplane. The design consisted of a simple linkage of cams and pushrods connected to the oil-pump drive of an Oberursel engine and the trigger of a Parabellum machine gun.
The technical problem that Fokker encountered was how to shoot between the rotating propeller blades. The two-bladed propeller revolved twelve hundred times per minute, so a blade would pass a given point twenty-four hundred times per minute. The firing rate of the Parabellum was six hundred rounds per minute. The solution to the problem involved keeping the pilot from pulling the trigger when the propeller blade was directly in front of the muzzle. The answer was to make the propeller shoot the gun.
During the testing trials, Fokker attached a small knob to the propeller that struck a cam as it revolved. The cam was attached to the hammer of the machine gun. Slow rotation of the propeller showed that the gun shot between the blades. To set the timing, Fokker attached a plywood disc to the propeller, and test firing continued until an even pattern of bullet holes appeared between the blades. One blade-mounted cam was found to be sufficient to operate the system, because the gun could shoot only six hundred times a minute, and the blades passed a given point twenty-four hundred times a minute. Fokker then attached a knee lever to the cam to operate a spring-held pushrod. A piece of the rod striking the gun hammer was hinged so that the pilot could engage the device when he was ready to shoot.
Fokker took his invention to Doberitz air base, and, after a series of exhausting trials before the German high command, both on the ground and in the air, he was allowed to take two prototypes of the machine-gun-mounted airplanes to Douai in German-held France. At Douai, two German pilots crowded into the cockpit with Fokker and were given demonstrations of the plane’s capabilities. The airmen were Oswald Boelcke, a test pilot and veteran of forty reconnaissance missions, and Max Immelmann, a young, skillful aviator who was assigned to the front. When the first two combat-ready versions of Fokker’s Eindecker 1 were delivered to the front lines, one was assigned to Boelcke and the other to Immelmann. On August 1, 1915, with their aerodrome under attack from nine English bombers, Boelcke and Immelmann manned their aircraft and attacked. Boelcke’s gun jammed, and he was forced to cut off his attack and return to the aerodrome. Immelmann succeeded in shooting down one of the bombers with his synchronized machine gun. It was the first victory credited to the Fokker-designed weapon system.
At the outbreak of World War I, military strategists and general high commands on both sides saw the wartime function of airplanes as a means to supply intelligence information behind enemy lines or as airborne artillery-spotting platforms. As the war progressed and aircraft flew more or less freely across the trenches, providing vital information to both armies, it became apparent to ground commanders that although it was important to obtain intelligence on enemy movements, it was also important to deny the enemy similar information. Early in the war, the French used airplanes as strategic bombing platforms. As both armies began to use their air forces for strategic bombing of troops, railways, ports, and airship sheds, it became evident that aircraft would have to be employed against enemy aircraft to prevent reconnaissance and bombing raids.
No aircraft in service to either army at the outset of World War I was intended officially for fighting. It was left to the pilot in a single-seat scoutcraft or to the observer in a two-seat observation plane to have a pistol or rifle on hand to defend himself and his craft if he encountered an enemy aircraft during a mission. Pistols, rifles, and shotguns loaded with chains, grenades, fléchettes (steel darts), rocks, and grappling hooks were all used in attempts to down enemy aircraft. It was apparent to most aviators that the ideal weapon for aerial combat was the machine gun. The problem was that no airplane in service at the war’s start was designed to carry such a weapon. Airplanes at that time were so fragile that the extra weight of a machine gun was enough to hamper their performance.
Two types of aircraft were in service to both armies: pusher-style planes with a propeller in the rear and tractor types with the propeller in the front. Although tractor types were faster, there was no means of mounting a machine gun in front of the pilot, where he could take aim, as a gun in that position would shoot off the blades of the propeller. A pusher plane with a machine gun mounted on the front offered the observer a wide field of fire forward, but his field to the sides and rear was obstructed by wings, struts, and wires. The observer also was forced to rely on the pilot to place him in proper firing position. Designers experimented with mounting machine guns on the sides of aircraft fuselages, on wing tops, and on swivel mounts, but these all denied the aviator the ability to use his aircraft as a means of aiming at a target.
With the invention of the synchronized forward-firing machine gun, pilots could use their aircraft as attack weapons. A pilot finally could coordinate control of his aircraft and his armaments with maximum efficiency. This conversion of aircraft from nearly passive observation platforms to attack fighters is the single greatest innovation in the history of aerial warfare. The development of fighter aircraft forced changes in military strategy, tactics, and logistics, ushering in the era of modern warfare. Fighter planes are responsible for the battle-tested military adage: Whoever controls the sky, controls the battlefield.
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Batchelor, John, and Bryan Cooper. Fighter: A History of Fighter Aircraft. New York: Charles Scribner’s Sons, 1974. A beautifully illustrated book on the history of fighter aircraft. Contains a set of diagrams showing the principles of the Fokker interrupter gear and the Garros Wedge. -
Bowen, Ezra, and the Editors of Time-Life Books. Knights of the Air. Alexandria, Va.: Time-Life Books, 1980. A richly illustrated volume documenting the rise of aerial warfare during World War I. Gives a good overview of the facts surrounding the development of the synchronized machine gun. -
Fokker, Anthony H. G., and Bruce Gould. Flying Dutchman: The Life of Anthony Fokker. New York: Holt, 1931. Fokker’s autobiography is easily read and well illustrated. Fokker’s contemporaries and historians have described him as a person of immense ego. In the chapter titled “I Invent the Synchronized Machine-Gun,” Fokker claims total credit for the idea, with no reference to the work of others. -
Grey, Charles G. The History of Combat Airplanes. Northfield, Vt.: Norwich University, 1942. Highly opinionated book by a contemporary of Fokker. A good reference point to learn about the military and political climate surrounding the invention of the synchronized machine gun. -
Lawson, Eric, and Jane Lawson. The First Air Campaign: August 1914-November 1918. 1996. Reprint. New York: Da Capo Press, 2002. Discusses all of the air warfare of World War I as though it was one long campaign, focusing on the race to develop new tactics and technologies. Includes maps, diagrams, bibliography, and index. -
Phelan, Joseph A. Heroes and Aeroplanes of the Great War, 1914-1918. New York: Grosset & Dunlap, 1973. Documents the lives and exploits of many early innovators in aerial combat tactics and illustrates the progression in fighter aircraft design throughout World War I.
Outbreak of World War I
World War I
Germany Begins Extensive Submarine Warfare
Germany Launches the First Zeppelin Bombing Raids
German Torpedoes Sink the Lusitania
United States Enters World War I