(515 kW) Mk4 Kestrel engine, which gave improved speed and rate of climb. Sidney Camm designed a monoplane version of the Fury in 1933. It was not developed until Rolls-Royce produced what became their famous Merlin engine. The design was then revised according to Air Ministry specification F5/34 to become the prototype Hawker Hurricane. Operational history The Fury I entered squadron service with the RAF in May 1931, re-equipping No. 43 Squadron. Owing to finance cuts in the Great Depression, only relatively small numbers of Fury Is were ordered, the type equipping No. 1 and 25 squadrons. At the same time, the slower Bristol Bulldog equipped ten fighter squadrons. The Fury II entered service in 1936–1937, increasing total number of squadrons to six. Furies remained with RAF Fighter Command until January 1939, replaced primarily with Gloster Gladiators and other types, such as Hawker Hurricane. After their front line service ended, they continued in use as trainers. The Fury was exported to several customers, being supplied with a variety of engines, including Kestrels, Hispano Suiza and Lorraine Petrel vee-type engines, Armstrong Siddeley Panther, Pratt & Whitney Hornet and Bristol Mercury radials. Three Furies were ordered by Spain in 1935, it being intended to produce another 50 under licence. The Spanish variant had a cantilever undercarriage design with Dowty internally sprung wheels, similar to that used on the Gladiator and was powered by a 612 hp (457 kW) Hispano Suiza 12Xbr engine, reaching a speed of 234 mph (377 km/h). The three Furies were delivered without armament on 11 July 1936, just before the outbreak of the Spanish Civil War. They were taken into service by the Spanish Republican Air Force, being fitted with machine guns salvaged from crashed aircraft. One Fury made a forced landing behind enemy lines due to a lack of fuel and was repaired by the Nationalists, although it was not used operationally, while the Republicans used one of the Furies in the defence of Madrid until wrecked in a crash in November 1936. Although withdrawn from RAF squadrons, the Fury was still used by some foreign air forces in the early 1940s; Yugoslav Furies saw action against Axis forces in the German invasion of 1941. On 6 April 1941, a squadron of Furies took off against the invading German Messerschmitt Bf 109Es and Messerschmitt Bf 110s. In the resulting air battle 10 Furies were destroyed, almost the