The B-25 was named in honor of General Billy Mitchell, a pioneer of U.S. military aviation. The B-25 is the only American military aircraft named after a specific person. By the end of its production, nearly 10,000 B-25s in numerous models had been built. These included a few limited variations, such as the US Navy's PBJ-1 patrol bomber and the Army Air Forces' F-10 photo reconnaissance aircraft
Design and development
Flight Performance School also included work in evaluating the performance of this B-25 Mitchell medium bomber
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 aircraft 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 Douglas DB-7 (later to be used by the US as the 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 11 April 1939. Nonetheless, the type was ordered into production, along with the Army's other new medium bomber, the Martin B-26 Marauder
Early production
Mitchell production in Kansas City in 1942
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 noticeable changes during this period included an increase in the size of the tail fins and a decrease in their inward cant.
A total of 6,608 B-25s were built at North American's Fairfax Airport plant in Kansas City, Kansas.
A descendant of the B-25 was the North American XB-28, meant to be a high-altitude version of the B-25. Despite this premise, the actual aircraft bore little resemblance to the Mitchell. It had much more in common with the B-26 Marauder.
Operational history
Lt. Peddy and crew, showing how many people were required to keep a B-25 flying
Doolittle Raid B-25Bs aboard USS Hornet
A B-25C being refueled
B-25 of 13th Squadron, 3rd Bomb Group, on low-level "skip-bombing" mission in New Guinea
B-25G Mitchell from the AAF TAC Center, Orlando, Florida, 17 April 1944
The B-25 first gained fame as the bomber used in the April 1942 Doolittle Raid, in which 16 B-25Bs, 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. However, 15 subsequently crash-landed en route to recovery fields in Eastern China. These losses were the result of fuel exhaustion, stormy nighttime conditions with zero visibility, and lack of electronic homing aids at the recovery bases. Only one landed intact; it came down in the Soviet Union, where its five-man crew was interned and the aircraft confiscated. Fortunately, 71 of 80 aircrew survived their historic mission and eventually made it back to American lines.
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 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 differed only in location of manufacture: -Cs at Inglewood, California, -Ds at Kansas City, Kansas. A total of 3,915 B-25Cs and -Ds 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 (parachute-retarded fragmentation bombs) missions against Japanese airfields in New Guinea and the Philippines. These heavily-armed Mitchells, field-modified by Major Paul I. "Pappy" Gunn, were also used on strafing and skip-bombing missions against Japanese shipping trying to re-supply their land-based armies. Under the leadership of Lt. Gen. George C. Kenney, B-25s of the Fifth and Thirteenth Air Forces devastated Japanese targets in the SWPA from 1942 to 1945, and played a significant role in pushing the Japanese back to their home islands. B-25s were also used with devastating effect in the Central Pacific, Alaska, North Africa, Mediterranean and China-Burma-India (CBI) theaters.
Because of the urgent need for hard-hitting strafer aircraft, a version 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-caliber weapon used operationally in an aircraft. 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 pilot. This was possible due to the shorter nose of the G-model and the length of the M4, which allowed the breech to extend into the navigator's compartment.
The B-25G's successor, the B-25H, had even more firepower. The M4 gun was replaced by the lighter T13E1, designed specifically for the aircraft. The 75 mm gun fired at a muzzle velocity of 2,362 fps (about 720 m/s). Due to its low rate of fire (approximately four rounds could be fired in a single strafing run) and relative ineffectiveness against ground targets, as well as substantial recoil, the 75 mm gun was sometimes removed from both G and H models and replaced with two additional .50-caliber machine guns as a field modification.[1] The -H also mounted four fixed forward-firing .50 in (12.7 mm) machine guns in the nose, four more fixed ones in forward-firing cheek blisters, two more in the top turret, one each in a pair of new waist positions, and a final pair in a new tail gunner's position. Company promotional material bragged the B-25H could "bring to bear 10 machine guns coming and four going, in addition to the 75mm cannon, a brace of eight rockets and 3000 pounds of bombs."[2]
The B-25H also featured a redesigned cockpit area, with the top turret moved forward to the navigator's compartment (thus requiring the addition of the waist and tail gun positions), and a heavily modified cockpit designed to be operated by a single pilot, the co-pilot's station and controls deleted, and the seat cut down and used by the navigator/cannoneer, the radio operator being moved to the aft compartment, operating the waist guns.[3] A total of 1,400 B-25Gs and B-25Hs were built in all.
The final version of the Mitchell, the B-25J, looked much like the earlier B, C and D, having reverted to the longer nose. The less-than-successful 75 mm cannon was deleted on the J model. Instead, 800 of this version were built with a solid nose containing eight .50 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 .50s: eight in the nose, four in under-cockpit packages, two in an upper turret, two in the waist, and a pair in the tail. No other bomber of World War II carried as many guns. However, the first 555 B-25Js (the B-25J-1-NC production block) were delivered without the fuselage package guns, because it was discovered muzzle blast from these guns was causing severe stress in the fuselage; while later production runs returned these guns, they were often removed as a field modification for the same reason.[4] 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 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.[5]
The Mitchell was also an amazingly sturdy aircraft and could withstand tremendous punishment. One well-known B-25C of the 321st Bomb Group was nicknamed "Patches" because its crew chief painted all the aircraft'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, straight-and-level flight required 8° of left aileron trim and 6° of right rudder, causing the aircraft to "crab" sideways across the sky.An interesting characteristic of the B-25 was its ability to extend range by using one-quarter wing flap settings. Since the aircraft normally cruised in a slightly nose-high attitude, about 40 U.S. 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 aircraft's range. [6]
Empire State Building accident
B-25C Mitchell
USAAF B-25C/D. Note the early radar fitted to the nose
Closeup of an early model B-25 gun pod
B-25J
B-25J warbird
B-25
The first version of the B-25 delivered. It was so badly needed that no prototype stages were ordered. The first nine aircraft 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. (Number made: 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. Re designated obsolete (RB-25A designation) in 1942. (Number made: 40.)
B-25B
Tail gunner eliminated; dorsal and ventral turrets added, each with a pair of .50-caliber 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. The Doolittle Raiders flew B-25Bs on their famous mission. (Number made: 120.)
B-25C
Improved version of the B-25B: upgraded from Wright R-2600-9 radials to R-2600-13 radials; de-icing and anti-icing equipment was added; the navigator received a sighting blister; and nose armament was increased to two .50-caliber 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 the Soviet Union. First mass-produced B-25. (Number made: 1,625.)
ZB-25C
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 3 January 1942. (Number made: 2,290.)
ZB-25D
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 aircraft was tested for almost two years, beginning in 1942; while the system proved extremely effective, no production models were built that used it before the end of World War II. Many prop aircraft today use the XB-25E system. (Number made: 1, converted.)
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