The first Master I was delivered to the Royal Air Force (RAF) in May 1939 and a total of 900 machines eventually built. Training Schools at Sealand, Monrose and Hullavington were the first to employ the type, although by September 1939, there were only seven machines in service.
The Rolls Royce Kestrel engine which powered the previous Miles M.9 Kestrel, was de-rated to a Mk.XXX engine which although it made the Master 70 mph (112,65 km/h) slower, it still had a top speed of 226 mph (364 km/h) at 15.000 ft (4.572 m) high. It could still outperform any other trainer aircraft in service.
Thanks to this speed and maneuverability, at the beginning of the Battle of Britain, a new armed sub-variant was designed, equipped with six 0.303 in machine guns, five more than a regular one. This 'Master Fighter' was slower than any other fighters, but it would have been useful in numbers as an emergency fighter. Around 24 machines were converted into fighters but, when the German threat diminished, the program was abandoned and they were converted back into fighters.
The first production Masters had a cockpit canopy with a vertical front to the windscreen that remained hinged. This was modified later to have a windscreen angled and opening to the side.
During Battle of Britain Master I was available to almost every operational squadron in the RAF. They were typically used to ferry pilots to the factories to pick up replacement aircraft or to collect shot down pilots who managed to land on an airfield. The Master was also used to land in open fields where anti-invasion obstacles could be quickly removed.
The Master I saw action during Battle of Britain too, although in the receiving end. On 16th August 1940 two German Junkers Ju.88 bombed the Flying Training School and Maintenance Unit at RAF Brize Norton, Oxfordshire, destroying no less than 46 Masters stationed there. Two day later, on 18th the Luftwaffe attacked RAF Kenley, southern London, destroying every hangar except one, destroying a Master, together with a Magister.
Both Air Ministry and Miles realized, back in 1939 that the supply of Kestrel engines would soon run out of supply as it had been out of production for six months, so Miles was asked to replace the Kestrel engine with the Bristol Mercury radial engine, as this engine was in mass production for aircraft such as the Bristol Blenheim or the Westland Lysander, among others.
The design was, therefore, modified in November 1939 and, after some testing, it was found that there were not enough Mercury engines available, so Miles was asked to change the design once again. This time the chosen engine was the American Pratt & Whitney Wasp Junior and the company denomination was Miles M.27 Master III, however, due to bureaucracy meddling, Air Ministry found that there were indeed, enough Mercury engines available for the Master II to be built, so a compromise was signed to produce both Master II and III.
The Master II was fitted with the aforementioned Bristol Mercury XX engine, yielding 870 hp of power, which made it 16 mph (26 km/h) faster than the Master I. The prototype flew for the first time in November 1939 and a total of 1.799 machines were build. It was produced at Miles factory in Woodley and continued at South Marston (where every Master III was produced. A total of 602 machines) until 1942, when it was decided to make way for the Miles Martinet.
Both Master II and III were equally used at Flying Training Schools as there was hardly any performance difference between them. If any, the Master III was 10 mph (16 km/h) slower. The main user was No.5 (Pilot) Advanced Flying Unit, based at Ternhill, Shropshire from 1942 onwards.
The Master II was also used as a glider tug. During 1942, when British Airborne forces were forming, some obsolete Hawker Audax and Hector biplanes were used to tow the GAL Hotspur training glider. This couldn't last long as as both aircraft were in short supply and the needs of the Glider Pilot Regiment were rapidly increasing. Miles was, therefore, asked if they could quickly convert a Master II into a glider tug and, just in one week a prototype was presented. This sub-variant had the bottom part of the rudder cut off and a tail hook, with its corresponding releasing mechanism installed in the cockpit.
A Master II was also adapted for firing rockets when these were made of general use in 1943. Rocket trails were fixed under both wings and a series of trials were carried out by the Aeroplane and Armament Experimental Establishment (A&AEE) at RAF Martlesham Heath.
Every version of the Master had provision for the upper section of the rear half of the canopy to open up in order to form a windscreen for the instructor, whose canopy was also equipped with an elevating seat to look forward during take off and landing and correct any mistakes. This, generally worked well except for the fact that, in speeds above 160 mph (258 km/h) the windscreen tend to shut itself, catching the rear occupant. The widescreen was also known to fly open during a spin giving the impression to the pupil that the had lost his instructor. Miles suggested a modification to avoid this with a permanent raised rear cockpit. The works on this were given the number M.31 and the resulting variant would've been called the Master IV, however, this idea didn't prosper as the Air Ministry wanted Miles to concentrate on the tug version of the Master.
Some other minor modifications concerned the wing tips which were rounded up in the Master I, but were square cut on later examples of Master II and III.
The Master III was kept in service until mid-1945 while it wasn't until November 1950 that the Master II was withdrawn from active service.
1. Scale Aircraft Modelling - vol.19 nº08 (1997.10) - Miles Military Trainers
2. https://en.wikipedia.org/wiki/Miles_Master
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