North American B-25 Mitchell

https://en.wikipedia.org/wiki/North_..._B-25_Mitchell

The North American B-25 Mitchell is a medium bomber that was introduced in 1941
and named in honor of Major General William "Billy" Mitchell, a pioneer of U.S.
military aviation. Used by many Allied air forces, the B-25 served in every
theater of World War II, and after the war ended, many remained in service,
operating across four decades. Produced in numerous variants, nearly 10,000
B-25s were built. These included a few limited models such as the F-10
reconnaissance aircraft, the AT-24 crew trainers, and the United States Marine
Corps' PBJ-1 patrol bomber.

Design and development

The Air Corps issued a specification for a medium bomber in March 1939 that was
capable of carrying a payload of 2,400 lb (1,100 kg) over 1,200 mi (1,900 km) at
300 mph (480 km/h) North American Aviation used its NA-40B design to develop the
NA-62, which competed for the medium bomber contract. No YB-25 was available for
prototype service tests. In September 1939, the Air Corps ordered the NA-62 into
production as the B-25, along with the other new Air Corps medium bomber, the
Martin B-26 Marauder "off the drawing board".

Early into B-25 production, NAA incorporated a significant redesign to the wing
dihedral. The first nine aircraft had a constant-dihedral, meaning the wing had
a consistent, upward angle from the fuselage to the wingtip. This design caused
stability problems. "Flattening" the outer wing panels by giving them a slight
anhedral angle just outboard of the engine nacelles nullified the problem, and
gave the B-25 its 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 tilt at their tops.

NAA continued design and development in 1940 and 1941. Both the B-25A and B-25B
series entered USAAF service. The B-25B was operational in 1942. Combat
requirements led to further developments. Before the year was over, NAA was
producing the B-25C and B-25D series at different plants. Also in 1942, the
manufacturer began design work on the cannon-armed B-25G series. The NA-100 of
1943 and 1944 was an interim armament development at the Kansas City complex
known as the B-25D2. Similar armament upgrades by U.S-based commercial
modification centers involved about half of the B-25G series. Further
development led to the B-25H, B-25J, and B-25J2. The gunship design concept
dates to late 1942 and NAA sent a field technical representative to the SWPA.
The factory-produced B-25G entered production during the NA-96 order followed by
the redesigned B-25H gunship. The B-25J reverted to the bomber role, but it,
too, could be outfitted as a strafer.


Role
Medium bomber

National origin
United States

Manufacturer
North American Aviation

First flight
19 August 1940

Introduction
1941

Retired
1979 (Indonesia)

Primary users
United States Army Air Forces
Royal Air Force
Soviet Air Force
United States Marine Corps

Number built
9,816

Developed from
North American NA-40

Developed into
North American XB-28


The majority of B-25s in American service were used in the war against Japan in
Asia and the Pacific. The Mitchell fought from the Northern Pacific to the South
Pacific and the Far East. These areas included the campaigns in the Aleutian
Islands, Papua New Guinea, the Solomon Islands, New Britain, China, Burma and
the island hopping campaign in the Central Pacific. The aircraft's potential as
a ground-attack aircraft emerged during the Pacific war. The jungle environment
reduced the usefulness of medium-level bombing, and made low-level attack the
best tactic. Using similar mast height level tactics and skip bombing, the B-25
proved itself to be a capable anti-shipping weapon and sank many enemy sea
vessels of various types. An ever-increasing number of forward firing guns made
the B-25 a formidable strafing aircraft for island warfare. The strafer versions
were the B-25C1/D1, the B-25J1 and with the NAA strafer nose, the J2 subseries.

The B-25B first gained fame as the bomber used in the 18 April 1942 Doolittle
Raid, in which 16 B-25Bs led by Lieutenant Colonel Jimmy Doolittle attacked
mainland Japan, four months after the bombing of Pearl Harbor. The mission gave
a much-needed lift in spirits to the Americans, and alarmed the Japanese, who
had believed their home islands to be inviolable by enemy forces. Although the
amount of actual damage done was relatively minor, it forced the Japanese to
divert troops for home defense for the remainder of the war.

The raiders took off from the carrier USS Hornet and successfully bombed Tokyo
and four other Japanese cities without loss. Fifteen of the bombers subsequently
crash-landed en route to recovery fields in eastern China. These losses were the
result of the task force being spotted by a Japanese vessel, forcing the bombers
to take off 170 mi (270 km) early, fuel exhaustion, stormy nighttime conditions
with zero visibility, and lack of electronic homing aids at the recovery bases.
Only one B-25 bomber landed intact, in Siberia, where its five-man crew was
interned and the aircraft confiscated. Of the 80 aircrew, 69 survived their
historic mission and eventually made it back to American lines.

Following a number of additional modifications, including the addition of
Plexiglas dome for navigational sightings to replace the overhead window for the
navigator and heavier nose armament, de-icing and anti-icing equipment, the
B-25C entered USAAF operations. Through block 20, the B-25C and B-25D differed
only in location of manufactu C series at Inglewood, California, and D series
at Kansas City, Kansas. After block 20, some NA-96s began the transition to the
G series, while some NA-87s acquired interim modifications eventually produced
as the B-25D2 and ordered as the NA-100. NAA built a total of 3,915 B-25Cs and
Ds 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 theatre in treetop-level
strafing and missions with parachute-retarded fragmentation bombs against
Japanese airfields in New Guinea and the Philippines. These heavily armed
Mitchells were field-modified at Townsville, Australia, under the direction of
Major Paul I. "Pappy" Gunn and North American technical representative Jack Fox.
These "commerce destroyers" were also used on strafing and skip bombing missions
against Japanese shipping trying to resupply their armies.

U.S. Navy and USMC

The U.S. Navy designation for the Mitchell was the PBJ-1 and apart from
increased use of radar, it was configured like its Army Air Forces counterparts.
Under the pre-1962 USN/USMC/USCG aircraft designation system, PBJ-1 stood for
Patrol (P) Bomber (B) built by North American Aviation (J), first variant (-1)
under the existing American naval aircraft designation system of the era. The
PBJ had its origin in an inter-service agreement of mid-1942 between the Navy
and the USAAF exchanging the Boeing Renton plant for the Kansas plant for B-29
Superfortress production. The Boeing XPBB Sea Ranger flying boat, competing for
B-29 engines, was cancelled in exchange for part of the Kansas City Mitchell
production. Other terms included the interservice transfer of 50 B-25Cs and 152
B-25Ds to the Navy. The bombers carried Navy bureau numbers (BuNos), beginning
with BuNo 34998. The first PBJ-1 arrived in February 1943, and nearly all
reached Marine Corps squadrons, beginning with Marine Bombing Squadron 413
(VMB-413). Following the AAFAC format, the Marine Mitchells had search radar in
a retractable radome replacing the remotely operated ventral turret. Later D and
J series had nose-mounted APS-3 radar; and later still, J and H series mounted
radar in the starboard wingtip. The large quantities of B-25H and J series
became known as PBJ-1H and PBJ-1J, respectively. These aircraft often operated
along with earlier PBJ series in Marine squadrons.

The PBJs were operated almost exclusively by the Marine Corps as land-based
bombers. To operate them, the U.S. Marine Corps established a number of Marine
bomber squadrons (VMB), beginning with VMB-413, in March 1943 at MCAS Cherry
Point, North Carolina. Eight VMB squadrons were flying PBJs by the end of 1943,
forming the initial Marine medium bombardment group. Four more squadrons were in
the process of formation in late 1945, but had not yet deployed by the time the
war ended.

Specifications (B-25H)

General characteristics
Crew: 5 (one pilot, navigator/bombardier, turret gunner/engineer, radio
operator/waist gunner, tail gunner)
Length: 52 ft 11 in (16.13 m)
Wingspan: 67 ft 7 in (20.60 m)
Height: 16 ft 4 in (4.98 m)
Wing area: 618 sq ft (57.4 m2)
Airfoil: root: NACA 23017; tip: NACA 4409R
Empty weight: 19,480 lb (8,836 kg)
Max takeoff weight: 35,000 lb (15,876 kg)
Powerplant: 2 × Wright R-2600-92 Twin Cyclone 14-cylinder two-row air-cooled
radial piston engines, 1,700 hp (1,300 kW) each

Performance
Maximum speed: 272 mph (438 km/h, 236 kn) at 13,000 ft (4,000 m)
Cruise speed: 230 mph (370 km/h, 200 kn)
Range: 1,350 mi (2,170 km, 1,170 nmi)
Service ceiling: 24,200 ft (7,400 m)

Armament

Guns: 12–18 × .50 in (12.7 mm) machine guns and 75 mm (2.95 in) T13E1 cannon
Hardpoints: 2,000 lb (900 kg) ventral shackles to hold one external Mark 13
torpedo
Rockets: racks for eight 5 in (127 mm) high velocity aircraft rockets (HVAR)
Bombs: 3,000 lb (1,360 kg) bombs



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