Editing Synchronization gear (section)

=== United States ===
French and British combat aircraft ordered for the [[American Expeditionary Force]] in 1917/18 were fitted with their "native" synchronization gears, including the Alkan-Hamy in Nieuports and [[Sopwith 1½ Strutter#In French service|French-built Sopwiths]], the Birkigt gear in SPADs, and the C.C. gear for British types. The C.C. was also adopted for the twin [[M1895 Colt–Browning machine gun#Marlin Rockwell M1917/M1918 versions|M1917/18 Marlin machine gun]]s fitted to the American built DH-4, and was itself made in America until the Nelson gear appeared in numbers.<ref name=Woodman17/>

==== The Nelson gear ====
The [[M1895 Colt-Browning machine gun#Marlin Rockwell M1917/M1918 versions|Marlin]] gas operated gun proved less amenable to synchronization than the Vickers. It was found that "rogue" shots occasionally pierced the propeller, even when the gear was properly adjusted and otherwise functioning well. The problem was eventually resolved by modifications to the Marlin's trigger mechanism,<ref name=BAP20>Bureau of Aircraft Production 1918, p. 20.</ref> but in the meantime the engineer [[Adolph Lincoln Nelson|Adolph L. Nelson]] at the Airplane Engineering Department at McCook Field had developed a new, mechanical gear especially adapted to the Marlin, officially known as the ''Nelson single shot synchronizer.''<ref name=Woodman18>Woodman 1989, pp. 199–200.</ref>  In place of the push rod common to many mechanical gears, or the "pull rod" of the Sopwith-Kauper, the Nelson gear used a cable held in tension for the transmission of firing impulses to the gun.<ref name=Woodman17/>

Production models were largely too late for use before the end of the First World War, but the Nelson gear became the post-war U.S. standard, as Vickers and Marlin guns were phased out in favour of the [[M1919 Browning machine gun|Browning .30 calibre machine gun]].

==== E-4/E-8 gears ====
The Nelson gear proved reliable and accurate, but it was expensive to produce and the necessity for its cable to be given a straight run could create difficulties when it was to be installed in a new type. By 1929 the latest model (the E-4 gear) had a new and simplified impulse generator, a new trigger motor, and the impulse cable was enclosed in a metal tube, protecting it, and permitting shallow bends. While the basic principle of the new gear remained unchanged: virtually all the components had been redesigned, and it was no longer officially referred to as the "Nelson" gear. The gear was further modernised in 1942 as the E-8. This final model had a modified impulse generator that was easier to adjust and was controlled from the cockpit by an electrical solenoid rather than a Bowden cable.