Editing V12 engine (section)

=== 1940s to present ===
[[File:YorkMerlin.JPG|thumb|1946 [[Rolls-Royce Merlin]] airplane engine in an [[Avro York]] ]]

V12 engines reached their apogee during [[World War II]] with engines such as the British [[Rolls-Royce Merlin]] and [[Rolls-Royce Griffon]], the Soviet [[Klimov VK-107]] and [[Mikulin AM-38]], the American [[Allison V-1710 engine|Allison V-1710]], and the German [[Daimler-Benz DB 600]] and [[Junkers#Junkers Jumo|Junkers Jumo]]. These engines generated about {{convert|1000|hp|kW|abbr=on|order=flip}} at the beginning of the war and over {{convert|1500|hp|kW|abbr=on|order=flip}} at their ultimate evolution stage. This rapid increase in power outputs was due to technology such as multi-speed [[supercharger]]s and high [[Octane rating|octane]] fuels, and the V12 layout was commonly adopted due to its low vibrations so that the powerful engines did not tear apart the light airframes of fighters.

The Allied forces used V12 engines with an "upright" design, while many German engines (aside from the [[BMW VI]], which was designed prior to World War II), used an [[Inline engine (aeronautics)#Inverted engine|inverted engine]] design, which had a lower centre of gravity and improved pilot visibility for single-engined designs. The only American-design inverted V12 engine of any type to see even limited service in World War II was the air-cooled [[Ranger V-770]], which was used in aircraft that were only used for training purposes within the United States, such as the [[Fairchild AT-21 Gunner]].

The Rolls-Royce Merlin V12 engine was used in several British aircraft including the [[Hawker Hurricane]] and [[Supermarine Spitfire]] fighters, and the [[Avro Lancaster]] and [[de Havilland Mosquito]] bombers. The Hurricane and Spitfire played vital roles in the [[Battle of Britain]]. The long, narrow configuration of the V12 contributed to good aerodynamics, while its smoothness allowed its use with relatively light and fragile airframes.

In the United States, the Rolls-Royce Merlin engine was produced under license by Packard Motor Car Company, which was used in the [[P-51 Mustang]] fighter. This engine was also incorporated into some models of the Curtiss P-40, specifically the P-40F and P-40L. Packard Merlins powered Canadian-built Hurricane, Lancaster, and Mosquito aircraft, as well as the UK-built [[Supermarine Spitfire (late Merlin powered variants)|Spitfire Mark XVI]], which was otherwise the same as the Mark IX with its British-built Merlin. The [[Allison V-1710]] was the only liquid-cooled V12 engine designed in the United States that was used on active service during World War II. It was initially used in the [[P-38 Lightning]], but the [[turbosupercharger]] system required bulky ductwork and had poor high-altitude performance. In 1943, a version using a more conventional mechanical [[supercharger]] began production.

After World War II, V12 engines became generally obsolete in aircraft due to the introduction of [[turbojet]] and [[turboprop]] engines that had more power for their weight, and fewer complications.