The Wellington Mk.X became the last production model of this particular bomber. Its design was based on the Mk.III's airframe, and it featured similar armament and equipment. The main difference was a new 1,675 hp Bristol Hercules Mk.VI (though some planes featured the Hercules Mk.XVI) fourteen-cylinder double-row air-cooled engine. There was also a difference less noticeable but not less important than the replaced engine: the switch to a new aluminum alloy with a better strength-to-specific gravity ratio. Using this alloy in the aircraft's structure allowed a higher take-off weight while preserving the Mk.III's flight characteristics.
Full-scale production of the Mk.X (Type 448) model started in the autumn of 1942, and it became the most popular plane in the Wellington family. A combined total of 3,803 aircraft were built. October 1945 saw the last of 11,461 Wellingtons.
In September 1939, the Wellingtons began to fight in Europe as long-distance scouts or as day-and-night bombers. From 1940 on, they were used only as night bombers. The aircraft began serving in North Africa in September 1940 and in the Far East in April 1942.
In 1942-43, the Wellington became the RAF Bomber Command's primary aircraft. Combat experience showed that it was the best of the three medium bombers used at that time. Its speed was faster than that of the Armstrong Whitworth Whitley, and its flight range was longer than that of the Handley Page Hampden, even though its bomb-carrying capacity was just as great. In the first «1,000 bomber raid» on Cologne on May 30, 1942, 599 of the 1,043 aircraft were Wellington bombers.
The Wellington bombers' last service in Western Europe was on the night of October 8, 1943. They were succeeded by heavy four-engine aircraft such as the Short Stirling, the Handley Page Halifax, and the Avro Lancaster, as the RAF Bomber Command increased its pressure on Germany.
In other theaters of operations, the aircraft was employed by the RAF until the end of the war. The anti-submarine Wellingtons sank a considerable number of the Axis powers' submarines. Production was discontinued in October 1945, and the plane was withdrawn from service in March 1953.