Editing Bristol Beaufighter (section)

===Prototypes and refinement===
On 17 July 1939, ''R2052'', the first, unarmed, prototype, conducted its [[maiden flight]], a little more than eight months after development had formally started.<ref name = "moyes 4"/> The rapid pace of development was partly due to the re-use of many elements of the Beaufort design, and frequently identical components. ''R2052'' was initially operated by Bristol for testing while it was based at [[Filton Aerodrome]].<ref name = "moyes 4"/> Early modifications to ''R2052'' included stiffening of the elevator control circuit, increased fin area and lengthening of the main [[oleo strut]] of the undercarriage to better accommodate weight increases and hard landings.<ref name = "moyes 4 5">Moyes 1966, pp. 4–5.</ref>

During the pre-delivery trials, the first prototype ''R2052'', powered by a pair of two-speed [[supercharged]] Hercules I-IS engines, had achieved 335&nbsp;mph (539&nbsp;km/h) at 16,800&nbsp;ft (5,120 m) in a clean configuration.<ref name = "moyes 5">Moyes 1966, p. 5.</ref> The second prototype, ''R2053'', which was furnished with Hercules I-M engines (similar to Hercules II) and was laden with operational equipment, had attained a lower speed of 309&nbsp;mph at 15,000&nbsp;ft. According to aviation author Philip Moyes, the performance of the second prototype was considered disappointing, particularly as the Hercules III engines of the initial production aircraft would likely provide little improvement, especially in light of additional operational equipment being installed; it was recognised that demand for the Hercules engine to power other aircraft such as the [[Short Stirling]] bomber posed a potential risk to the production rate of the Beaufighter. This sparked considerable interest in the adoption of alternative engines for the type.<ref name = "moyes 4 5"/>

[[File:252 Squadron RAF Beaufighter cockpit at Chivenor IWM CH 17305.jpg|thumb|left|Cockpit of a Beaufighter Mk.IF]]
[[Roy Fedden]], chief designer of the Bristol engine division, was a keen advocate for the improved Hercules VI for the Beaufighter but it was soon passed over in favour of the rival Griffon engine, as the Hercules VI required extensive development.<ref name = "moyes 5"/> Due to production of the Griffon being reserved for the [[Fairey Firefly]], the Air Ministry instead opted for the [[Rolls-Royce Merlin]] to power the Beaufighter until the manufacturing rate of the Hercules could be raised by a new [[shadow factory]] in [[Accrington]]. The standard Merlin XX-powered aircraft was later called the ''Beaufighter Mk.IIF''; the planned slim-fuselage aircraft, alternatively equipped with Hercules IV and Griffon engines, the ''Beaufighter Mk.III'' and ''Beaufighter Mk.IV'' respectively, were not built.<ref name = "moyes 5"/>

In February 1940, an order was placed for three Beaufighters, converted to use the alternative Merlin engine. The Merlin engine installations and [[nacelle]]s were designed by [[Rolls-Royce Limited|Rolls-Royce]] as a complete "[[power egg]]"; the design and approach of the Beaufighter's Merlin installation was later incorporated into the design for the much larger four-engined [[Avro Lancaster]] bomber.<ref name="white 64"/> Success with the Merlin-equipped aircraft was expected to lead to production aircraft in 1941.<ref name="white 64"/> In June 1940, the first Merlin-powered aircraft conducted its first flight. In late 1940, the two Merlin-equipped prototypes (the third having been destroyed in a bombing raid) were delivered.<ref name = "moyes 5 10">Moyes 1966, pp. 5, 10.</ref> Flight tests found that the Merlins left the aircraft underpowered, with a pronounced tendency to swing to port, making take-offs and landings difficult and causing a high accident rate&nbsp;– out of 337 Merlin-powered aircraft, 102 were lost to accidents.<ref name="white 64">White 2006, p. 64.</ref><ref name = "moyes 10"/>

On 2 April 1940, ''R2052'' was delivered to the RAF; it was followed by ''R2053'' two weeks later.<ref name = "moyes 5"/> On 27 July 1940, the first five production Beaufighters were delivered to the RAF along with another five on 3 August 1940. These production aircraft incorporated aerodynamic improvements, reducing [[aerodynamic drag]] from the engine nacelles and tail wheel; the oil coolers were also relocated on the [[leading edge]] of the wing.<ref name = "moyes 5"/> The armament of the Beaufighter had also undergone substantial changes, the initial 60-round capacity spring-loaded drum magazine arrangement being awkward and inconvenient; alternative systems were investigated by Bristol.<ref name = "moyes 5 6"/>

Bristol's proposed [[recoil]]-operated ammunition feed system was rejected by officials, which led to a new system being devised and tested on the fourth prototype, ''R2055''. The initial rejection was later reversed, upon the introduction of a new electrically driven feed derived from [[Manufacture d'armes de Châtellerault|Châtellerault]] designs brought to Britain by [[Free French]] officers, which was quite similar to Bristol's original proposal.<ref name = "moyes 6"/> The initial 50 production aircraft were approved for completion with a cannon-only armament. The design of the cannons and the armament configuration was revised on most aircraft. The addition of six [[M1919 Browning machine gun#Browning 03 Mark II|.303 Browning]] [[machine gun]]s made the Beaufighter the most heavily armed fighter aircraft in the world, capable of delivering a theoretical weight of fire of up to {{convert|780|lb|kg|abbr=on}} per minute; the practical rate of fire was much lower due to gun overheating and ammunition capacity.<ref name = "moyes 6"/>

Further armament trials and experimental modifications were performed throughout the Beaufighter's operational life. By mid-1941, 20 Beaufighters were reserved for test purposes, including engine development, stability and manoeuvrability improvements and other purposes.<ref name = "moyes 5 11 13">Moyes 1966, pp. 5, 11, 13.</ref> In May 1941, the Beaufighter Mk.IIs ''R2274'' and ''R2306'' were modified to the ''Beaufighter Mk.III'' standard; removing the six wing guns and two inboard cannons to install a [[Boulton-Paul]]-built four-gun turret behind the pilot, to overcome the effect of recoil and nose-down tendency when firing the usual armament, was found to obstruct the emergency egress of the pilot.<ref name = "moyes 11"/> The fourth prototype, ''R2055'', had its regular armament replaced by a pair of {{nowrap|40 mm}} guns for attacking ground targets, a [[Vickers S]] gun mounted on the starboard fuselage and a [[Rolls-Royce 40mm Cannon|Rolls-Royce BH]] gun mounted on the port fuselage; these trials also led to the Vickers gun being installed on an anti-tank [[Hawker Hurricane]] IID.<ref name = "moyes 5 11 13"/>