World War II: North American B-25 Mitchell

B-25 Mitchell
B-25 Mitchell flying low over the desert. US Air Force

The evolution of the North American B-25 Mitchell began in 1936 when the company began work on its first twin-engine military design. Dubbed the NA-21 (later NA-39), this project produced an aircraft that was of all-metal construction and powered by a pair of Pratt & Whitney R-2180-A Twin Hornet engines. A mid-wing monoplane, the the NA-21 was intended to carry a payload of 2,20o lbs. of bombs with range of around 1,900 miles.

Following its first flight in December 1936, North American modified the aircraft to correct several minor issues. Re-designated the NA-39, it was accepted by the US Army Air Corps as the XB-21 and entered into competition the following year against an improved version of the Douglas B-18 Bolo. Further altered during the trials, the North American design proved to have consistently superior performance to its competitor, but cost significantly more per aircraft ($122,000 vs. $64,000). This led to the USAAC passing on the XB-21 in favor of what became the B-18B.

Development

Utilizing the lessons learned from the project, North American moved forward with a new design for a medium bomber which was dubbed the NA-40. This was spurred on in March 1938 by USAAC circular 38-385 which called for a medium bomber capable of carrying a payload of 1,200 lbs. a distance of 1,200 miles while maintaining a speed of 200 mph.

First flying in January 1939, it proved under-powered. This issue was soon remedied through the use of two Wright R-2600 Twin Cyclone engines.

The improved version of the aircraft, the NA-40B, was placed into competition with entries from Douglas, Stearman, and Martin, where it performed well but failed to secure an USAAC contract.

Seeking to take advantage of Britain and France's need for a medium bomber during the early days of World War II, North American intended to build the NA-40B for export. These attempts failed when both countries elected to move forward with a different aircraft.

In March 1939, as the NA-40B was competing, the USAAC issued another specification for a medium bomber requiring a payload of 2,400 lbs., range of 1,200 miles, and a speed of 300 mph. Further revising their NA-40B design, North American submitted the NA-62 for evaluation. Due to a pressing need for medium bombers, the USAAC approved the design, as well as the Martin B-26 Marauder, without conducting the usual prototype service tests. A prototype of the NA-62 first flew on August 19, 1940.

Design & Production

Designated B-25 Mitchell, the aircraft was named for Major General Billy Mitchell. Featuring a distinctive twin tail, early variants of the B-25 also incorporated a "greenhouse"-style nose which contained the bombardier's position. They also possessed a tail gunner position at the rear of the aircraft. This was eliminated in the B-25B while a manned dorsal turret was added along with a remotely operated ventral turret. Around 120 B-25Bs were built with some going to the Royal Air Force as the Mitchell Mk.I.

Improvements continued and the first type to be mass-produced was the B-25C/D.

This variant increased the aircraft's nose armament and saw the addition of improved Wright Cyclone engines. Over 3,800 B-25C/Ds were produced and many saw service with other Allied nations. As the need for effective ground support/attack aircraft increased, the B-25 frequently received field modifications to fulfill this role. Acting on this, North American devised the B-25G which increased the number of guns on the aircraft and included the mounting of a 75 mm cannon in a new solid nose section. These alterations were refined in the B-25H.

In addition to a lighter 75 mm cannon, the B-25H mounted four .50-cal. machine guns below the cockpit as well as four more in cheek blisters. The aircraft saw the return of the tail gunner position and the addition of two waist guns.

Capable of carrying 3,000 lbs. of bombs, the B-25H also possessed hard points for eight rockets. The final variant of the aircraft, the B-25J, was a cross between the B-25C/D and the G/H. It saw the removal of the 75 mm gun and the return of the open nose, but the retention of the machine gun armament. Some were built with a solid nose and an increased armament of 18 machine guns.

B-25J Mitchell Specifications:

General

  • Length: 52 ft. 11 in.
  • Wingspan: 67 ft. 6 in.
  • Height: 17 ft. 7 in.
  • Wing Area: 610 sq. ft.
  • Empty Weight: 21,120 lbs.
  • Loaded Weight: 33,510 lbs.
  • Crew: 6

Performance

  • Power Plant: 2 × Wright R-2600 Cyclone radials, 1,850 hp
  • Combat Radius: 1,350 miles
  • Max Speed: 275 mph
  • Ceiling: 25,000 ft.

Armament

  • Guns: 12-18 × .50 in (12.7 mm) M2 Browning machine guns
  • Bombs: 6,000 lbs. max. or 8 x 5" rockets & 3,000 lbs. bombs

Operational History

The aircraft first came to prominence in April 1942 when Lieutenant Colonel James Doolittle used modified B-25Bs in his raid on Japan. Flying from the carrier USS Hornet (CV-8) on April 18, Doolittle's 16 B-25s struck targets in Tokyo, Yokohama, Kobe, Osaka, Nagoya, and Yokosuka before flying on to China. Deployed to most theaters of the war, the B-25 saw service in the Pacific, North Africa, China-India-Burma, Alaska, and the Mediterranean. Though effective as a level medium bomber, the B-25 proved particularly devastating in Southwest Pacific as a ground attack aircraft.

Modified B-25s routinely conducted skip bombing and strafing attacks against Japanese ships and ground positions.

Serving with distinction, the B-25 played key roles in Allied victories such as the Battle of the Bismarck Sea. Employed throughout the war, the B-25 was largely retired from frontline service at its conclusion. Though known as a forgiving aircraft to fly, the type did cause some hearing loss problems among crews due to engine noise issues. In the years after the war, the B-25 was used by a number of foreign nations.

Format
mla apa chicago
Your Citation
Hickman, Kennedy. "World War II: North American B-25 Mitchell." ThoughtCo, Dec. 11, 2017, thoughtco.com/north-american-b-25-mitchell-2361514. Hickman, Kennedy. (2017, December 11). World War II: North American B-25 Mitchell. Retrieved from https://www.thoughtco.com/north-american-b-25-mitchell-2361514 Hickman, Kennedy. "World War II: North American B-25 Mitchell." ThoughtCo. https://www.thoughtco.com/north-american-b-25-mitchell-2361514 (accessed December 12, 2017).