B-25 Mitchell

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The B-25 Mitchell was an American twin-engined medium bomber manufactured by North American Aviation. It was used with devastating effect against German and Japanese targets in every combat theater of World War II. The aircraft was named the 'Mitchell' in honour of General Billy Mitchell, an early airpower pioneer and advocate of an independent United States Air Force. By the end of its production, more than 10,000 B-25's in several models had been built. These included a few limited variations, such as the U.S. Navy's PBJ-1 patrol bomber and the Army Air Force's F-10 photo reconnaissance aircraft.

The B-25 was flown by a number of Allied forces in addition to the Army Air Force and the U.S. Navy. These nations included Australia, the United Kingdom (which received more than 900), China, The Netherlands, and Russia.

The B-25 first gained fame as the bomber used in the April 1942 Doolittle Raid, in which 16 B-25B's, led by the legendary Lt Col Jimmy Doolittle, took off from the carrier USS Hornet and successfully bombed Tokyo and four other Japanese cities without loss to themselves. However, 15 of the planes subsequently crash-landed in Eastern China enroute to their recovery fields in that country. These losses were the result of fuel exhaustion, stormy nighttime conditions with zero visibility, and the lack of electronic homing aids at the recovery bases. Only one B-25B landed intact; it came down in Russia, where its five-man crew was interned and the aircraft confiscated. Fortunately, the majority of the 80 Doolittle Raid crewmen survived their historic mission and eventually made it back to American lines.

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Development

The B-25 was a descendant of the earlier XB-21 (North American-39) project of the mid-1930s. Experience gained in developing that aircraft was eventually used by North American in designing the B-25 (called the NA-40 by the company). One NA-40 was built, with several modifications later being done to test a number of potential improvements. These improvements included Wright R-2600 radial engines, which would become standard on the later B-25.

In 1939, the modified and improved NA-40B was submitted to the United States Army Air Corps for evaluation. This plane was originally intended to be an attack bomber for export to the United Kingdom and France, both of which had a pressing requirement for such aircraft in the early stages of World War II. However, those countries changed their minds, opting instead for the also-new Douglas A-20 Havoc. Despite this loss of sales, the NA-40B re-entered the spotlight when the Army Air Corps evaluated it for use as a medium bomber. Unfortunately, the NA-40B was destroyed in a crash on 1939 April 11. Nonetheless, the type was ordered into production, along with the Army's other new medium bomber, the Martin B-26 Marauder.

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Early production

An improvement of the NA-40B, dubbed the NA-62, was the basis for the first actual B-25. Due to the pressing need for medium bombers by the Army, no experimental or service-test versions were built. Any necessary modifications were made during production runs, or to existing aircraft at field modification centers around the world.

A significant change in the early days of B-25 production was a re-design of the wing. In the first nine aircraft, a constant-dihedral wing was used, in which the wing had a consistent, straight, slight upward angle from the fuselage to the wing tip. This design caused stability problems, and as a result, the dihedral angle was nullified on the outboard wing sections, giving the B-25 its slightly gull wing configuration. Less noticible changes during this period included an increase in the size of the tail fins and a decrease in their inward cant.

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Operational history

Following a number of additional modifications, including the addition of Plexiglas windows for the navigator and radio operator, heavier nose armament, and de-icing and anti-icing equipment, the B-25C version was released to the Army. This was the second mass-produced version of the Mitchell, the first being the lightly-armed B-25B used by the Doolittle Raiders. The B-25C and B-25D were identical, the only difference being their location of manufacture. The B-25C was built in Inglewood, California, while the B-25D was made in Kansas City, Kansas. A total of 3,915 B-25Cs and B-25Ds were built by North American during World War II.

Although the B-25 was originally designed to bomb from medium altitudes in level flight, it was used frequently in the Southwest Pacific Theater (SWPA) on treetop-level strafing and parafrag missions against Japanese airfields in New Guinea and the Philippines. These heavily-armed Mitchells, field-modified by engineering genius Major "Pappy" Gunn, were also used on strafing and skip-bombing missions against Japanese shipping trying to re-supply their land-based armies. Under the brilliant leadership of Lt Gen George C. Kenney, B-25's of the 5th and 13th Air Forces devastated Japanese targets in the SWPA from 1942 to 1945, and played a signifcant role in pushing the Japanese back to their home islands. B-25's were also used with devastating effect in the Central Pacific, Alaska, North Africa, Mediterranean, and China-Burma-India theaters.

Because of the urgent need for hard-hitting strafer aircraft, a version of the B-25 dubbed the B-25G was developed, in which the standard-length transparent nose --- and the bombardier --- were replaced by a shorter, solid nose containing two fixed .50-calibre machine guns and a 75 mm M4 cannon. The latter was the largest calibre weapon ever used in an American bomber. The cannon was manually loaded and serviced by the navigator, who was able to perform these operations without leaving his crew station just behind the pilots. This was possible due to the shorter nose of the G-model and the long length of the M4, which allowed the gun's breech to extend into the navigator's compartment. The B-25G’s successor, the B-25H, had even more firepower: six fixed forward-firing .50-calibre machine guns, two more in the top turret, one each in a pair of new waist positions, and a final two in a new tail gunner's position. Fourteen hundred B-25Gs and B-25Hs were built.

The final version of the Mitchell, the B-25J, looked much like the earlier B, C, and D models, having reverted to the longer nose section as used in those types. The less-than-successful 75mm cannon was deleted on the J model. Instead, 800 of this version were built with a solid nose containing eight .50-caliber machine guns, while other J-models featured the earlier ‘greenhouse’ style nose containing the bombardier's position. Regardless of the nose style used, all J-models also included two .50 caliber guns in a "fuselage package" located directly under the pilot's station, and two more such guns in an identical package just under the co-pilot's compartment. The solid-nose B-25J variant carried an impressive total of 18 .50-caliber guns: eight in the nose, four in under-cockpit packages, two in an upper turret, two in the waist compartment, and a pair in the tail position. No other bomber of World War II carried as many guns. In all, 4,318 B-25Js were built.

The B-25 was a safe and forgiving aircraft to fly. With an engine out, 60° banking turns into the dead engine were possible, and control could be easily maintained down to 145 mph (230 km/h). The tricycle landing gear made for excellent visibility while taxiing. The Mitchell was also an amazingly sturdy aircraft that could withstand tremendous punishment. One well-known B-25C of 321st Bomb Group was nicknamed "Patches" because its crew chief painted all the plane's flak hole patches with high-visibility zinc chromate paint. By the end of the war, this aircraft had completed over 300 missions, was belly-landed half a dozen times, and sported over 400 patched holes. The airframe was so bent that straight-and-level flight required 8° of left aileron trim and 6° of right rudder, causing the aircraft to "crab" sideways across the sky. The only significant complaint about the B-25 was the extremely high noise level produced by its engines; as a result, many pilots eventually suffered from various degrees of hearing loss (Higham 1978).

An interesting characteristic of the B-25 was that its range could be extended by using one-quarter wing flap settings. Since the aircraft normally cruised in a slightly nose-high attitude, about 40 US gallons (150 l) of fuel was below the fuel pickup point and thus unavailable for use. The flaps-down setting gave the aircraft a more level flight attitude, which resulted in this fuel becoming available, thus slightly extending the plane's range (Higham 1975).

The B-25 is featured in the book Catch-22, and in the movies "Thirty Seconds over Tokyo" (one pilot's account of the Doolittle Raid), Pearl Harbour, and Catch-22(film), which features a large number of B-25s in flying condition. A meticulously restored B-25, painted and marked as Jimmy Doolittle's aircraft, is on permanent display at the Air Force Museum in Dayton, Ohio.

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De-icing tests

In 1942, two B-25Cs were converted to test aircraft in order to investigate de-icing and anti-icing equipment; these planes were redesignated 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 the metal surfaces. Both were tested extensively until 1944; the XB-25E system was extremely reliable and more practical than the XB-25F system.

While the results of the tests on the XB-25E were promising, no aircraft during World War II was built to utilise that system, although it is commonly used today. Most propeller-driven 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 engines is blown through these tubes, and melts away any ice formations on the wings.

The further history of the XB-25F is unknown, but the sole XB-25E (42-32281) was scrapped.

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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 bore little resemblance to the Mitchell. It was much more similar to the B-26 Marauder.

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Units Using the B-25 during World War II:

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United States Army Air Forces

Fifth Air Force (Southwest Pacific): 3rd, 22nd, 38th, 345th Bomb Groups.

Seventh Air Force (Central Pacific): 41st Bomb Group.

Ninth Air Force (North Africa and Mediterranean): 12th and 340th Bomb Groups.

Tenth Air Force (China-Burma-India): 12th and 341st Bomb Groups and 1st Air Commando Group.

Eleventh Air Force (Aleutian Islands, Alaska): 28th Composite Group.

Twelfth Air Force (North Africa and Mediterranean): 12th, 310th, 321st, 340th Bomb Groups.

Thirteenth Air Force (Southwest Pacific): 42nd Bomb Group.

Fourteenth Air Force (China-Burma-India): 1st Bomb Group (Chinese-American Composite Wing) and 341st Bomb Group (from Tenth Air Force, November 1944).


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Royal Air Force

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Royal Australian Air Force

  • Number 18 (Netherlands East Indies) Squadron
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Variants and Design stages

  • B-25—The first version of the B-25 delivered. It was so badly needed that 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 the dihedral angle was eliminated on the outboard section. (×24)
  • B-25A—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—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). 23 were delivered to the RAF as the Mitchell Mk I.(×120)
  • B-25C— 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 the United Kingdom as the Mitchell II, and in Canada, China, The Netherlands, and Russia. First mass-produced B-25. (×1625)
  • B-25D— 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—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—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—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—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. One B-25G was passed to the British, who gave it the name Mitchell II that had been used for the B-25C. (×420)
  • B-25H—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—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—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-25J—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.
  • CB-25J - Utility transport version.
  • ZB-25C -
  • ZB-25D -
  • ZXB-25E -
  • PBJ-1C - Similar to the B-25C for the US Navy. Often fitted with airborne search radar and used in the anti-submarine role.
  • PBJ-1D - Similar to the B-25D for the US Navy. Differed in having on a single .50 caliber M2 in the tail turret and beam gun positions similar to the B-25H. Often fitted with airborne search radar and used in the anti-submarine role.
  • PBJ-1G - US Navy designation for the B-25G
  • PBJ-1H - US Navy designation for the B-25H
  • PBJ-1J - US Navy designation for the B-25J-NC (Blocks -1 through -35) with improvements in radio and other equipment. Often fitted with "package guns" and wingtip search radar for the anti-shipping/anti-submarine role.
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Operators

  • Australia, Bolivia, Brazil, Canada, China, Chile, Colombia, Cuba, France, Indonesia, Mexico, Netherlands, Netherlands East Indies, Peru, Soviet Union, Uruguay, United Kingdom, United States (Army Air Corps, Army Air Force, Air Force, Marine Corps, Navy), Venezuela,
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Specifications (B-25J)

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References

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Museum displays

B-25J "Briefing Time"
B-25J
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External links

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Related content

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