B-25 Mitchell

B-25 Mitchell, England, 2001

B-25 Mitchell was a twin-engined, medium bomber manufactured by North American Aviation in the United States and used during World War II. By the time production of the plane ended, roughly 10,000 had been built, including PBJ-1 Navy Patrol Bomber and an F-10 reconnaissance version. It served in every combat theatre and was used by a number of countries other than the United States, including Australia, Britain (which received more than 900), China, The Netherlands, and Russia. Its nickname 'Mitchell' was in honour of General Billy Mitchell, an early proponent of airpower.

While the B-25 was meant originally to bomb from medium altitudes in level flight, it was used frequently in the Pacific Theatre in treetop-level missions against Japanese airfields and for operations such as strafing and skip-bombing against enemy Japanese shipping.

The B-25 is most famous as the bomber used in the 1942 Doolittle Raid, where the raiders took off from the aircraft carrier USS Hornet, bombed Tokyo, and crashed in China; a B-25 also collided with the Empire State Building in 1945. The B-25 is the aircraft featured in the popular and influential novel Catch-22 and subsequent film.

Contents

1 Development

2 Early Production

3 Operational History

4 De-Icing Test

5 XB-28

6 Units Using the B-25

6.1 United States Army Air Force
6.2 Royal Air Force
6.3 Royal Australian Air Force

7 Variants and Design stages

8 Specifications (B-25J)

8.1 General Characteristics
8.2 Performance
8.3 Armament

9 References

10 External links

11 Related Content

Development

The B-25 was a descendant of the aborted XB-21 (N[orth]A[merican]-39) project of the mid-1930s. Experience gained in making the XB-21 was used by North American in designing the B-25 (NA-40). One NA-40 was built; several modifications were made on it to test a number of potential features, including the replacement of its Pratt & Whitney R-1830 radials with Wright R-2600 radials, the engine type that would become standard on the B-25.

The product of these experimentations, dubbed the NA-40B, was submitted to the United States Army Air Corps for evaluation near the end of the 1939. It was intended to be an attack bomber, to be exported to Britain and France, both of which had a pressing requirement for such aircraft in the early stages of World War II. However, the NA-40B was passed up in favour of the plane that would become the A-20 Havoc. Despite this loss, the NA-40B re-entered the spotlight when the Army evaluated it for use as a medium bomber. Unfortuantely, the plane was destroyed in a crash on 1939 April 11. Nonetheless, the NA-40B design was ordered for production in 1939.

Early Production

Along with the B-26 Marauder, the B-25 was ordered by the Army for production in 1939. An improvement on the NA-40B, dubbed the NA-62, was the basis for the first B-25 version. Due to a desperate need for medium bombers, no experimental or service-test versions were built. Any necessary modifications were made during production runs, or to existing aircraft at field modification centres.

The most significant change was a rearrangement of the wing. In the first nine aeroplanes of the production line, a dihedral wing was used. This design had some stability issues, so the dihedral angle was nullified on the outboard section of the wing, giving the B-25 a distinct 'gull wing' configuration. One less important change was an increase in the size of the vertical stabilisers and a decrease in the inward cant.

Operational History

Following a number of modifications, including improved engines, a sighting blister for the navigator, more nose armament, and de-icing and anti-icing equipment, the B-25C was released to the Army. It was the first mass-produced version of the B-25. The B-25D was identical, except in location: where the B-25C was built in Inglewood, California, the B-25D was built in Kansas City, Kansas. A total of 3915 B-25Cs and B-25Ds were built by North American during the course of the war.

Because of extreme need for durable aircraft to use in strafing missions, a version of the B-25 dubbed the B-25G was developed, in which the transparent nose was replaced by a solid nose. This housed two fixed .50-calibre machine guns and a 75 mm M4 cannon, the largest calibre weapon ever used on an American bomber. The B-25G’s successor, the B-25H, had even more firepower with the addition of 6 fixed .50-calibre machine guns. 1400 B-25Gs and B-25Hs were built.

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B-25_Flying.jpg

The last produced version, the B-25J, was somewhere between the B-25C and the B-25H. It maintained much of the fixed armament of the B-25H, but the solid nose was replaced by a ‘greenhouse’ one seen on earlier models, though 800 B-25Js were converted to a solid nose version. It also featured improved engines. 4318 B-25Js were built.

De-Icing Test

In 1942, two B-25Cs were converted to test aircraft to investigate de-icing and anti-icing equipment; they were redesignated the XB-25E and XB-25F. The XB-25E (nicknamed ‘Flamin’ Maimie’) used engine exhaust gases circulated through chambers in the wing to melt ice. The XB-25F used insulated electrical coils, to heat metal surfaces. Both were tested extensively until 1944; the XB-25E system was found extremely reliable and practical (more practical than the XB-25F system).

While the results of tests on the XB-25E were promising, no aircraft during World War II was built that utilised that system. It is now a common method today. Most prop planes used by the United States Air Force use so-called ‘piccolo tubes’ that run along the leading edges of the wings. Hot air bled from the engine is blown through those tubes, and melts any ice that may form on the wing.

The further history of the XB-25F is unknown, but when the sole XB-25E (42-32281) was scrapped the nose-section was saved by the Commemorative Air Force, Midland, Texas.

XB-28

A descendant of the B-25 was the XB-28 Dragon, meant to be a high-altitude version of the B-25. Despite this premise, the actual aircraft evolved to be little like the Mitchell. It was much more similar to the B-26 Marauder.

Units Using the B-25

United States Army Air Force

12th Bomb Group
17th Bomb Group

Royal Air Force

Number 98 Squadron
Number 180 Squadron
Number 226 Squadron
Number 305 Squadron
Number 320 Squadron
Number 342 Squadron
Number 681 Squadron
Number 684 Squadron

Royal Australian Air Force

Number 18 (Netherlands East Indies) Squadron

Variants and Design stages

B-25 (http://www.wpafb.af.mil/museum/research/bombers/b3-2.htm)—The first version of the B-25 delivered. It was so badly needed, no prototype stages were ordered. The first nine planes were built with constant dihedral angle. Due to low stability, the wing was redesigned so that it the dihedral angle was eliminated on the outboard section. (×24)
B-25A (http://www.wpafb.af.mil/museum/research/bombers/b3-3.htm)—Version of the B-25 modified to make it combat ready; additions included self-sealing fuel tanks, crew armour, and an improved tail gunner station. No changes were made in the armament. Redesignated obsolete (RB-25A designation) in 1942. (×40)
B-25B (http://www.wpafb.af.mil/museum/research/bombers/b3-4.htm)—Tail gunner eliminated; dorsal and ventral turrets added, each with a pair of .50-calibre machine guns. The ventral turret was retractable, but the increased drag still reduced the cruise speed by 30 mph (48 km/h). (×120)
B-25C (http://www.wpafb.af.mil/museum/research/bombers/b3-5.htm)— Improved version of the B-25B: upgraded from Wright R-2600-9 radials to R-2600-13 radials; deicing and anti-icing equipment was added; the navigator received a sighting blister; and nose armament was increased to two .50-calibre machine guns, one fixed and one flexible. The B-25C model was the first mass produced B-25 version; it was also used in Britain as the 'Mitchell II', and in Canada, China, The Netherlands, and Russia. First mass-produced B-25. (×1625)
B-25D (http://www.wpafb.af.mil/museum/research/bombers/b3-6.htm)— Identical to the B-25C. The only difference was that the B-25C was made in Inglewood, California whereas the B-25D was made in Kansas City, Kansas. First flew on 1942 January 3. (×2290)
XB-25E (http://www.wpafb.af.mil/museum/research/bombers/b3-7.htm)—Single B-25C modified to test de-icing and anti-icing equipment that circulated exhaust from the engines in chambers in the leading and trailing edges and empennage. The plane was tested for almost two years, beginning in 1942; while the system proved extremely effective, no planes were built that used it before the end of World War II. Many prop planes today use the XB-25E system. (×1, converted)
XB-25F (http://www.wpafb.af.mil/museum/research/bombers/b3-8.htm)—A modified B-25C that tested the use of insulated electrical de-icing coils mounted inside the wing and empennage leading edges as a de-icing system. The hot air de-icing system tested on the XB-25E was more practical. (×1, converted)
XB-25G (http://www.wpafb.af.mil/museum/research/bombers/b3-9.htm)—Modified B-25C in which the transparent nose was replaced by a solid one, with two fixed .50-calibre machine guns and a 2.95-calibre (75 mm) M4 Cannon, the largest weapon ever carried on an American bomber. (×1, converted)
B-25G (http://www.wpafb.af.mil/museum/research/bombers/b3-10.htm)—To satisfy the dire need for ground-attack and strafing aircraft, the B-25G was made following the success of the prototype XB-25G. The production model featured increased armour and a greater fuel supply than the XB-25G. (×400)
B-25H (http://www.wpafb.af.mil/museum/research/bombers/b3-11.htm)—An improved version of the B-25G. It featured two more fixed .50-calibre machine guns in the nose, and four in fuselage-mounted pods; the heavy M4 cannon was replaced by a lighter 2.95-calibre (75 mm) T13E1. (×1000)
B-25J (http://www.wpafb.af.mil/museum/research/bombers/b3-12.htm)—The last production model of the B-25, often called a cross between the B-25C and the B-25H. It had a transparent nose, but many of the delivered planes were modified to have a solid nose. Most of its 14-18 machine guns were forward-facing for strafing missions. 316 were delivered to the Royal Air Force as the ‘Mitchell III’. (×4318)
TB-25 (http://www.wpafb.af.mil/museum/research/bombers/b3-13.htm)—A trainer variant; most models of the B-25 were used at some point as training aircraft.
- TB-25D—Originally designated AT-24A (Advanced Trainer, Model 24, Version A). Trainer modification of B-25D. 60 AT-24s were built in total.
- TB-25G—Originally designated AT-24B. Trainer modification of B-25G. 60 AT-24s were built in total.
- TB-25C—Originally designated AT-24C. Trainer modification of B-25C. 60 AT-24s were built in total.
- TB-25J—Originally designated AT-24D. Trainer modification of B-25J. 60 AT-24s were built in total, and another 600 B-25Js were modified after the war.
- TB-25K—Hughes E1 fire-control radar trainer (Hughes). (×117)
- TB-25L—Hayes pilot-trainer conversion. (×90)
- TB-25M—Hughes E5 fire-control radar trainer. (×40)
- TB-25N—Hayes pilot-trainer conversion. (×47)
VB-25 (http://www.wpafb.af.mil/museum/research/bombers/b3-14.htm)—A number of B-25s were converted for use as staff and VIP transports. Henry H. Arnold and Dwight D. Eisenhower both used converted B-25Js as their personal transports.

Specifications (B-25J)

General Characteristics

Crew: 6
Length: 52 ft 11 in (16.1 m)
Wingspan: 67 ft 6 in (20.6 m)
Height: 17 ft 7 in (4.8 m)
Wing area: 610 ft² (57 m²)
Empty: 21,120 lb (9,580 kg)
Loaded: 33,510 lb (15,200 kg)
Maximum takeoff: 41,800 lb (19,000 kg)
Powerplant: 2× Wright R-2600 'Cyclone' radials, 1,850 hp (1,380 kW)

Performance

Maximum speed: 275 mph (442 km/h)
Cruising speed: 230 mph (370 km/h)
Combat Range: 1,350 miles (2,170 km)
Ferry Range: 2,700 miles (4,300 km)
Service ceiling: 25,000 ft (7,600 m)
Rate of climb: 790 ft/min (240 m/min)
Wing loading: 55 lb/ft² (270 kg/m²)
Power/Mass: .110 hp/lb (.182 kW/kg)

Armament

12× .50-calibre machine guns
3,200 lb (1,800 kg) bombs

References

External links

Detailed historical overview (http://www.b25.net)
Fantasy of Flight's B25 (http://www.fantasyofflight.com/aircraftpages/b25.htm)