The Merlin: The engine that saved the free world?
For most people, an engine just gets us from A to B - and drinks expensive petrol.
But one, the Rolls-Royce Merlin, may have been the difference between freedom and tyranny.
Such is its lasting impact, it was celebrated on Sunday with the first ever Spitfires, Merlins and Motors event at Duxford - the Imperial War Museum's aviation centre in Cambridgeshire.
Mike Evans, who founded the Rolls-Royce Heritage Trust, believes the engine turned the tide of war.
"Without the Merlin, we would not have won the Battle of Britain and Hitler may have crossed the channel," he said.
Designed in Derby, it powered a series of planes which between 1940 and 1945 halted, hammered and then crippled the forces of Nazi Germany.
The Merlin had a rich heritage, developed from engines designed and used during World War I and the peacetime air speed competition, the Schneider Trophy.
Receiving no government backing, Rolls-Royce built a prototype which by 1935 was producing more than 1,000 horsepower, 40% more than its predecessor the Kestrel.
This performance led to it being adopted for the new generation of RAF fighters - just in time for Britain's hour of greatest need in 1940.
Leo McKinstry, author of books on the Spitfire, Hurricane and Lancaster, said: "By preventing the Luftwaffe from gaining air supremacy over southern England, the two legendary fighters destroyed the Reich's hopes of mounting an invasion.
"But these aircraft would never have achieved that success without the Rolls-Royce Merlin engine.
"Robust and supremely efficient, the Merlin gave the RAF's fighters the power and performance they needed to defend our skies."
Proven in combat, demand for the Merlin grew. Production was expanded to factories in Crewe, Glasgow and Manchester - and eventually the US.
Mr Evans said: "People had confidence in it and it went on and on being improved.
"A lot of other manufacturers were shouting that they had the best thing since sliced bread saying 'forget the Merlin, it is old hat'.
"But it got better and better as the war went on. It was there, it could be relied upon, it would work."
Once Britain was safe from invasion, attention turned to striking back through Bomber Command - but its planes often suffered savage losses.
However, from late 1941 the Lancaster, powered by four Merlins, gave the RAF the ability hit the Third Reich hard.
Mr McKinstry said: "With its vast capacity, capable of carrying 22,000 pounds, the Lancaster needed a special engine and, as the epitome of reliability, the Merlin was ideally suited to the task.
"It was, of course, the Merlin that powered the planes of the Dambusters Raid in May 1943, the greatest single RAF exploit of the war and one that symbolised Britain's heroic fightback against Germany."
Even with the Lancaster, the RAF concentrated mainly on night attacks. Darkness protected the planes but made accurate bombing difficult.
The United States Air Force decided on daylight attacks but some raids suffered losses of more than 20%.
The answer was to protect the bombers with the sleek, silver Mustang fighter - but its impact was not instant.
Peter Murton, research officer at Duxford, said: "The American P-51 Mustang was only successful as a high-altitude escort fighter because the original American Allison engine was replaced with a Merlin - at the recommendation of the Air Fighting Development Unit here at Duxford.
"This created the most potent and successful long-range escort fighter of the war."
Using the Mustang, the fighting power of the Luftwaffe was broken in a matter of weeks in early 1944.
'Hope and Glory'
By the end of the war, and the emergence of the jet engine, about 150,000 Merlins had been built. It was used in 17 operational aircraft types.
Mr Murton said: "The Merlin was fundamental to the success of the Allied air campaign.
"If you think about the aircraft types that were fitted with the Merlin and were successful in particular because of their power plants, it was crucial."
And its legacy continues, as Mr Evans explained: "It's like Land of Hope and Glory, it's part of who we are.
"I was at an American airshow at their base in Mildenhall and the commentator called for quiet, for all other engines to be stopped and said 'Let's just listen to the Merlin'."