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F/Lt Peter Baxter recalls his experience with the history of Merlin Engines in Lancaster Bombers....

A little background information on the development of the Merlin engine would probably be of interest. The Lancaster started life in 1941 when the Mark I was developed from the ill-fated Manchester, and was fitted with four Merlin XX engines of 1,280 horsepower. By the middle of 1942, Rolls Royce could not supply sufficient engines to meet the demand, bearing in mind that the Merlin was used in many types of aircraft including Spitfires; even the 18,000 per year rate by 1943 was not enough! So, attention was focused on the possibility of producing them in America as well. The Ford company was approached, but they could not agree to help, and eventually Packard stepped in. The drawings were already in America having been sent there at the fall of France, but much work remained to be done before production could commence, and the drawing staff had to work night and day to prepare working drawings from the master copies. Packards went into production in a big way, clearing their car-producing lines (for three-quarters of a mile!) and then installing completely new tools. When they started to make the engines they found some difficulty in working to Rolls Royce tolerances, but still managed to produce their first engine within a year.

The American Merlins developed 1,460 hp, and were designated Merlin XXVIII; at first they were fitted with a Bendix carburettor because the British S.U. could not be produced in time, but eventually the Stromberg carburettor became standard. Another important difference with the introduction of the Packard engine, was the use of rounded-end propellors, known as paddle blades. These props improved performance, particularly in the climb, and they were later adopted on all Lancasters. With the Merlin XXVIII came magnificent tool sets, which were much appreciated by the ground crews. The Lancaster manufacturers were allotted specific quantities of British and American engines, so that in general, the serial numbers of the aircraft were a guide to the initial engine installation, although in service, when an engine was changed, it could have been replaced by either type. The aircraft was originally designated a Mk I or Mk III respectively. A Lancaster Mk II was also introduced during 1942, this version being fitted with Bristol Hercules radial engines (as an insurance against delay in supplies of Merlins from America), but as I did not fly in this type I am not qualified to pass comment on it. Continuous improvement was made to the Merlin engine as time passed, and it eventually produced over 2,000 hp; each succeeding modification allowed us to go faster or higher or carry a heavier bomb load, but never was it more apparent than on take-off when the boost pressure was increased from +12 in 1942 to +18 in 1945 (a 50% advance). I honestly expected the engines to blow apart at this extreme power, which was coupled with excruciating noise, and never was I more thankful to throttle back than when we had attained sufficient height!

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