The problem of firing a machine gun through a spinning propeller was, in theory, straightforward. A bullet passing through the arc swept by the propeller blades would, under most circumstances, shatter the blade and destroy the aircraft. The solution — synchronizing the gun so that it fired only when the blade was not in the path of the bullet — had been contemplated by several aviation engineers before the First World War. The question was who would solve it first, and what advantage they would gain.

The answer arrived in the summer of 1915 in the form of the Fokker Eindecker, a modest monoplane of no particular distinction except for one feature: Anthony Fokker's Stangensteuerung interrupter gear, which synchronized a Spandau LMG 08 machine gun with the engine's firing cycle. The result was an aircraft that could aim its gun simply by pointing the aircraft at the target. Between the summer of 1915 and early 1916, this advantage produced what RFC pilots named, with bleak accuracy, the Fokker Scourge.

The Technical Problem and Fokker's Solution

The concept of a synchronizer had been discussed before the war. French pilot Roland Garros had used a different approach in early 1915: armoring the propeller blades with steel deflectors so that bullets that would otherwise shatter the wood were deflected away. It was crude and inefficient, but it worked well enough that Garros shot down several German aircraft before being forced down behind German lines in April 1915.

His aircraft, with its armored propeller still attached, was sent to Anthony Fokker's factory at Schwerin. Fokker, a Dutch aviation designer working under contract for the German military, spent approximately 48 hours developing an interrupter mechanism considerably more sophisticated than the French deflector system. Rather than armoring the blades, Fokker's gear used cams driven by the engine shaft to interrupt the firing mechanism whenever a blade was in the line of fire. The result was a gun that fired between the blades at any engine speed — a true synchronizer.

The Fokker E.I, carrying this system, entered operational service with German Feldflieger Abteilungen in the summer of 1915.

The Scourge

German pilots Max Immelmann and Oswald Boelcke were among the first to fly the Eindecker in combat, and their results were immediate and alarming. Between August 1915 and March 1916, the Fokker E-series aircraft dominated the airspace above the Western Front in a way no previous aircraft had. RFC loss rates climbed sharply. British pilots flying BE.2c aircraft — a stable, slow reconnaissance plane designed to hold steady for photography, not maneuver — found themselves unable to escape or fight back against the diving Fokker attacks.

The tactics developed by Boelcke — the diving attack from above and behind, breaking away before the enemy could respond — were formally codified in his Dicta Boelcke, a set of aerial combat principles that remained influential for decades. The Eindecker topped out at approximately 130 mph at sea level, but its synchronized armament gave it an insurmountable tactical advantage over contemporary Allied aircraft, most of which still relied on observers with manually aimed Lewis guns.

"We were being sent up in machines which were of an obsolete type and quite unfit to meet the enemy," wrote RFC pilot Cecil Lewis in his memoir Sagittarius Rising. "The feeling of being hunted, of being at the mercy of a faster and more maneuverable machine, was something one did not easily forget."

The British parliamentary record contains sharp exchanges in the House of Commons during this period, with critics of the war ministry demanding to know why pilots were being sent to their deaths in aircraft incapable of defending themselves. The phrase "Fokker fodder" entered common usage in the RFC.

The Allied Response

The British and French response came in two forms: technical and tactical. On the technical side, both nations accelerated development of synchronized firing systems. The British Sopwith Aviation Company developed a synchronizer independently; by mid-1916 the Sopwith Pup and later the Camel would carry British-synchronized Vickers guns. The French developed the Nieuport 11, which sidestepped the propeller problem entirely by mounting a Lewis gun on the upper wing, firing over the propeller arc — a workable solution that appeared in early 1916.

On the tactical side, the RFC began experimenting with formation flying, reasoning that a group of aircraft could provide mutual covering fire in ways that a lone BE.2c could not. This was the origin of the RFC's eventual doctrine of squadron-sized formations — a practice that would define aerial tactics for the rest of the war and beyond.

The Scourge effectively ended by the spring of 1916 as Allied synchronized fighters entered service in quantity. Immelmann was killed in June 1916 — the circumstances remain disputed, with some accounts suggesting his own synchronizer malfunctioned. Boelcke survived until October 1916, when a mid-air collision with one of his own wingmen brought him down over the Somme. He had accumulated 40 victories.

The Broader Significance

The Fokker Scourge demonstrated, for the first time at scale, that technological asymmetry in aviation could produce not merely tactical disadvantage but operational crisis. The lesson was absorbed — unevenly and imperfectly — by all major air powers and informed the frantic aviation arms races that characterized both interwar development and the Second World War.

The synchronizer itself was rapidly proliferated. By 1917, every major combatant nation had developed its own version. The deflector approach was abandoned. Interrupter and synchronizer gears became standard equipment on all fighter aircraft, and remained so until jet propulsion removed the propeller from the equation entirely.

Fokker himself emerged from the war having sold synchronizers to both sides — the Allies eventually purchased examples of his gear for evaluation. He emigrated to the United States after the war and continued building aircraft, including the famous Fokker Tri-Motor, until his death in 1939. The machine that started it all, the Eindecker, was obsolete within eighteen months of its introduction. That is the normal pace of technological war.