It is very appropriate that as the Rolls-Royce Owners’ Club, you have chosen to have your dinner under this great Mk1 Lancaster, “G for George”, which is powered by four Rolls-Royce Merlin1 aero engines.

George is part of a special object theatre display Striking by night, which represents a tribute to all our RAAF aircrew in Bomber Command. The dangers those crews faced at night over occupied Europe were extraordinary: adverse weather, anti-aircraft fire, the threat of night fighters, collisions with others in the bomber stream, bombs falling from other aircraft above – and then navigating a way back, sometimes with a damaged aircraft, to an airfield hopefully not fogged in. It’s no wonder the losses in aircrew were so high. But one thing I’m told was constant: the reliability of the Merlin engine.

The Rolls-Royce Merlin was used not only on the Avro Lancaster bomber. Indeed, the first aircraft types to use the then newly-developed Merlin were the Hawker Hurricane, the Vickers Supermarine Spitfire, and the Fairey Battle. Two of these aircraft were extraordinarily successful; without a doubt, the Battle of Britain could not have been won without the Hurricane and Spitfire. In due course, the Merlin was to be used in a variety of types, including the Armstrong Whitworth Whitley, de Havilland Mosquito and Hornet, Avro Lancaster, Avro York, Avro Lincoln, Bolton Paul Defiant, and the Fairey Fulmar.

Some Handley Page Halifax bombers had Merlins, although the normal fit for that aircraft was a magnificent, 14-cylinder radial engine with sleeve valves, the Hercules. The ultimate development of that, the Bristol Centaurus, can be seen in our Aircraft Hall on the Sea Fury, which I believe represents the apogee of single-engine fighter development. Some of the naval variant of the Spitfire, the Seafire, also had Merlins, some Beaufighters did, and the Vickers Wellington bomber had them as well.

Now, that’s just a list of British aircraft, and I won’t claim it to be fully comprehensive, as all sorts of expedient things happen in wartime. Elsewhere, the US Curtiss P-40F Warhawk had a Merlin, as did the North American P-51 Mustang. This was a Packard Merlin, manufactured in the US under licence. Merlin applications didn’t end when the war was over. In post-war Spain, local versions of the German Heinkel 111 and Bf-109 were fitted with Merlins. The total production of Merlins is believed to be over 150,000 of all marks, and in the UK they came off five separate production lines.

A complete list of all Merlin variants doesn’t seem to be available (or at least my research did not uncover one), but I can account for 50 variants from the Mark 1 up to a Merlin 85 (as a matter of interest, the mark numbers do not seem to be sequential). Then there was a Merlin 102 for the Lincoln bomber, which was produced in Australia, and I have noted also 130/131, 224/225, as well as 500, 600 and 700 series. I’m sure there’s a PhD in researching all the mark numbers and specifying the engineering differences!

 On thinking about it, and reading some contemporary reports, perhaps the reason there were so many marks lay in Rolls-Royce’s policy of continually introducing into the production line the developments necessary for improved performance and reliability. This was done in what one engineer described as “digestible quantities”2, so that completely new marks of engine evolved all the time. This practice could lead to logistic problems, and possibly that is why cannibalisation was such a common practice on some airfields.

However, there’s no doubt all the developments yielded significant performance improvements. The brake horsepower (hp) of the Merlin went from 1,000 in 1939 to 2,100 in 1944, and if you look at performance tables, a Spitfire went from a maximum speed of 340 miles per hour in 1939 to 430 mph in 1944. That is a significant increase in anyone’s language. In 1939 a Spitfire could be at 20,000 feet in 10 minutes; in 1944 it would be at almost 40,000 feet in the same time.3

So how was this done during the life of the Merlin engine? As it happened, Rolls-Royce had long, well-established prior experience with in-line V12 engines, going back to an aero engine called the Kestrel. The Kestrel was in due course developed into the Peregrine (700 hp), and an engine called the Vulture (1,700 hp). Both these developments, although satisfactory, did not power any overwhelmingly successful aircraft. In fact, the Vulture was used on the Manchester bomber, a failed forerunner of the Lancaster.

Rolls-Royce saw the need for a 1,000 hp engine, and went ahead with its development as a private venture. This was a far-sighted decision which helped the British war effort immeasurably. The company used 35 prototypes in the development of this engine. Some were used in, of all things, a German Heinkel 70 aircraft, which had the advantage of an enclosed cabin in which engineers could sit and monitor the performance of the prototype engines.4 Cooling problems encountered during trials were overcome eventually with the use of US-sourced ethylene glycol.5 There were also reliability problems in the Mark 1 version that required a major improvement program to overcome. By then the Air Ministry had become interested in the Merlin, initially because it needed a more powerful engine for its planned new fighter aircraft.

Over its life, the Merlin’s big improvements in performance came about for essentially two reasons. Supercharging was introduced, which successfully went from a single stage – single speed version, to a single stage – two speed version, and finally to two stages and two speeds. The other factor that gave the big improvement was the use of improved fuels. Of course, mechanical improvements were necessary to accommodate the additional stresses imposed by supercharging and enhanced fuels.6 The interesting thing is that during all of these improvements, there was no change in the engine’s compression ratio, its displacement (1,065 cubic inches, or 27 litres) or its rpm (a nominal 3,000).

Well, there you have it. It’s a fascinating story of a celebrated British development. As a mechanical engineer more interested in gas turbines when younger, I have to say that I never appreciated fully the contribution of the Merlin until I came to the Memorial and learnt more about it. The development of the Merlin is a great success story, which I’m sure you are pleased to know about as Rolls-Royce owners and enthusiasts.


  1. The Merlin is named after a small falcon, rather than King Arthur’s magician Merlin.
  2. A.C. Lovesey, De Havillard Aircraft Company, “Development of the Rolls-Royce Merlin from 1939 to 1945”, presentation, November 1945
  3. Lovesey
  4. After my talk, a gentleman introduced himself and said his father (a Rolls-Royce employee in the Second World War) had long ago told him about the Germans gaining access to the Merlin during these trials. Apparently special markings had been tampered with. However, it was a Mark 1, which had cooling and reliability problems.
  5. John Dell and Martin Waligorski, “The Development of Rolls-Royce Merlin Engine”, Wikipedia, posted 10 April 2010.
  6. Lovesey


The assistance of AWM Senior Curator John White is gratefully acknowledged.




Sunday 10 April 2011


Steve Gower