By any standards, the 27 litre, twelve-cylinder Rolls-Royce Merlin engine may be described as excellent, and will forever be associated with the Spitfire, despite powering other classic and well known aircraft such as the Hurricane and Lancaster as well as not so well known types such as the Defiant. However, the designers at Rolls-Royce were well aware that the Merlin engine, good as it was, had a finite development life. Shortly after the outbreak of war in September 1939, Rolls-Royce began development of a new engine, which was based on the Merlin. Later christened Griffon, the new engine also had twelve cylinders, but had a capacity of 36.7 litres with an output of l,700hp (l,267k\V) as compared to the Merlin II which powered the early Spitfire Mk Is of l,030hp (768kw). Naturally, such an engine would be larger, and consequently heavier, than its predecessor, but the genius of Rolls-Royce was such that the Griffon was only 3in (7.5cm) longer, its frontal area only 6% greater, and its weight only 6001b (272kg) heavier than that of the Merlin. This meant that the standard Spitfire airframe could accommodate the new engine, provided that the engine mountings were strengthened and the oil tank repositioned, and therefore a whole new branch of the Spitfire family tree could be conceived and developed to utilise it.
