new U.S. landplane designs were tractor biplanes, with pushers of all types becoming regarded as old fashioned on both sides of the Atlantic. However, new pusher designs continued to be designed right up to the armistice, such as the Vickers Vampire, although few entered service after 1916.. At least up to the end of 1916, however, pushers (such as the Airco DH.2 fighter) were still favoured as gun-carrying aircraft by the British Royal Flying Corps, because a forward-firing gun could be used without being obstructed by the arc of the propeller. With the successful introduction of Fokker's mechanism for synchronising the firing of a machine gun with the blades of a moving propeller, followed quickly by the widespread adoption of synchronisation gears by all the combatants in 1916 and 1917, the tractor configuration became almost universally favoured and pushers were reduced to the tiny minority of new aircraft designs that had a specific reason for using the arrangement. Both the British and French continued to use pusher configured bombers, though there was no clear preference either way until 1917. Such aircraft included (apart from the products of the Farman company itself) the Voisin bombers (3,200 built), the Vickers F.B.5 "Gunbus", and the Royal Aircraft Factory F.E.2, however even these would find themselves being shunted into training roles before disappearing entirely. Possibly the last fighter to use the Farman pusher configuration was the 1931 Vickers Type 161 COW gun fighter. During the long eclipse of the configuration the use of pusher propellers continued in aircraft which derived a small benefit from the installation and could have been built as tractors. Biplane flying boats, had for some time often been fitted with engines located above the fuselage to offer maximum clearance from the water, often driving pusher propellers to avoid spray and the hazards involved by keeping them well clear of the cockpit. The Supermarine Walrus was a late example of this layout. The so-called push/pull layout, combining the tractor and pusher configurations—that is, with one or more propellers facing forward and one or more others facing back—was another idea that continues to be used from time to time as a means of reducing the asymmetric effects of an outboard engine failure, such as on the Farman F.222, but at the cost of a severely reduced efficiency on the rear propellers, which were often smaller and attached to lower-powered engines as a