From 'Flying Guns WW1':
"Work continued on the gun installations and G. H. Challenger designed the first of the ring-type mountings, which emerged in the early summer of 1915. This was further refined to include a complex spring-type balancing system, but was eventually replaced in British service by the Scarff type, which was introduced in 1916 and became the standard ring mounting thereafter."
The Scarff continued in RAF use well into the 1930s, although it was supplemented by some proprietary mountings of similar type, such as the Fairey 'high-speed' mounting.
Tony Williams: Military gun and ammunition website