North American B-25 Mitchell

With the release of the United States Army Air Corps Circular Proposal No 39-640 on the 11th March 1939 which called for a twin-engined bomber North American submitted their NA-40 design protected by 0.30-in machine-guns positioned in the nose, dorsal and ventral areas and able to carry a 1,200lb bomb load and featuring tricycle landing gear and it would take 195,000 engineering man hours to produce the first example of the aircraft.

Flying for the first time in January 1939 the prototype, piloted by Paul Balfour, was powered by a pair of 1,100-hp Pratt & Whitney R-1830-S6C3-G engines. But the NA-40-2 appeared with power being provided by 1,300-hp Wright CR-2600-A71 Cyclone engines and this aircraft was sent to be evaluated by the USAAC at Wright Field but due to pilot error would crash two weeks later. During this time however the potential of the aircraft impressed the USAAC so much that North American was asked to develop the aircraft to serve in the medium bomber role and this was re-designated NA-62 and the basic design was completed in September 1939, with 184 aircraft ordered into production by the USAAC that same month under the designation B-25 and named after William 'Billy' Mitchell. However it would still be another eleven months before the type first flew when a B-25 took to the skies on the 19th August 1940.

The production version of the B-25 featured a number of improvements over the prototypes now being powered by the 1,700-hp Wright Cyclone radial engine, a rear gun being installed and a wider fuselage, after the 25th aircraft onwards the B-25A appeared featuring armour plating for the crew and self sealing tanks and it would be the B-25A which would enter operational service first based at McChord Field as part of the 17th Bombardment Group and would also achieve the B-25s first operational success when a Japanese submarine was sunk on the 24th December 1941 off the US West Coast.

With power-operated dorsal and ventral turrets with two 0.50-in machine-guns each the B-25B appeared, and a number of these were sent to Australia during 1942 serving as part of the 3rd Bombardment Group. It would be the B-25B featuring modifications such as autopilot and a 60% increase in fuel capacity that would take part in the famous 'Doolittle Raid'. Sixteen aircraft would take off from the aircraft carrier USS Hornet (CV-8) to attack various targets in Japan before landing back in China.

The B-25C followed featuring increased bomb load and autopilot and this was followed by the B-25D which was essentially similar. Entering service in February 1944 the B-25G was designed to attack Japanese shipping and had a 75-mm M4 US Army cannon supplemented by two 0.50-in guns mounted in the nose. The B-25H would be the most heavily armed version of the Mitchell, still featuring a 75-mm cannon, although this was a lighter T13E1 model, four 0.50-in guns mounted in the nose, two gun blisters either side of the fuselage with a 0.50-in machine gun and a pair of these were also in the rear gun. The B-25H could also carry a torpedo on top of its 3,000lb bomb load as could its successor the last production Mitchell the B-25J, which had its cannon replaced by four more 0.50-in machine-guns, had its fuselage guns removed and could also carry eight 5-in rockets.

As well as serving with the US armed forces the Royal Air Force would also use the North American B-25 Mitchell in high numbers to replace its Douglas Boston and Lockheed Ventura aircraft and the type entered operational service with the RAF on the 22nd January 1943 when six aircraft from No. 180 Squadron attacked the oil installations at Ghent, Belgium, three would fail to return. As well as the RAF B-25 Mitchells would serve with various air forces around the world including Canada, Netherlands and China.

By the time production had finished 9,984 B-25s had been built and served in various roles including reconnaissance and wing de-icing experiments and continued in service outside of the US until 1960.