North American B-25 Mitchell

The North American B-25 Mitchell is an American medium bomber that was introduced in 1941 and named in honour 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 theatre 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 several limited models such as the F-10 reconnaissance aircraft, the AT-24 crew trainers, and the United States Marine Corps’ PBJ-1 patrol bomber.

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”.

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 centres 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.

After the war, the USAF placed a contract for the TB-25L trainer in 1952.

This was a modification program by Hayes of Birmingham, Alabama.

Its primary role was reciprocating engine pilot training.

A development of the B-25 was the North American XB-28 Dragon, designed as a high-altitude bomber.

Two prototypes were built with the second prototype, the XB-28A, evaluated as a photo-reconnaissance platform, but the aircraft did not enter production.

Variants

B-25

The initial production version of B-25s, they were powered by 1,350 hp (1,007 kW) R-2600-9 engines and carried up to 3,600 lb (1,600 kg) of bombs and defensive armament of three .30 machine guns in nose, waist, and ventral positions, with one .50 machine gun in the tail.

The first nine aircraft were built with constant dihedral angle.

Due to low stability, the wing was redesigned so that the dihedral was eliminated on the outboard section.

B-25A

This version of the B-25 was 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.

It was redesignated obsolete (RB-25A) in 1942.

B-25B

The tail and gun position were removed and replaced by a manned dorsal turret on the rear fuselage and retractable, remotely operated ventral turret, each with a pair of .50 in (12.7 mm) machine guns.

A total of 23 were supplied to the Royal Air Force as the Mitchell Mk I.

B-25C

An improved version of the B-25B, its powerplants were upgraded from Wright R-2600-9 radials to R-2600-13s; de-icing and anti-icing equipment were added; the navigator received a sighting blister; and nose armament was increased to two .50 in (12.7 mm) 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 Mk II), in Canada, China, the Netherlands, and the Soviet Union.

B-25D

Through block 20, the series was near identical to the B-25C.

The series designation differed in that the B-25D was made in Kansas City, Kansas, whereas the B-25C was made in Inglewood, California.

Later blocks with interim armament upgrades, the D2s, first flew on 3 January 1942.

F-10

The F-10 designation distinguished 45 B-25Ds modified for photographic reconnaissance.

All armament, armour, and bombing equipment were stripped.

Three K.17 cameras were installed, one pointing down and two more mounted at oblique angles within blisters on each side of the nose.

Optionally, a second downward-pointing camera could also be installed in the aft fuselage.

Although designed for combat operations, these aircraft were mainly used for ground mapping.

B-25D weather reconnaissance variant

In 1944, four B-25Ds were converted for weather reconnaissance.

One later user was the 53d Weather Reconnaissance Squadron, originally called the Army Hurricane Reconnaissance Unit, now called the “Hurricane Hunters”.

Weather reconnaissance first started in 1943 with the 1st Weather Reconnaissance Squadron, with flights on the North Atlantic ferry routes.

XB-25E

A single B-25C was 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.

XB-25F-A

A modified B-25C, it used insulated electrical coils mounted inside the wing and empennage leading edges to test the effectiveness as a de-icing system.

The hot air de-icing system tested on the XB-25E was determined to be the more practical of the two.

XB-25G

This modified B-25C had the transparent nose replaced to create a short-nosed gunship carrying two fixed .50 in (12.7 mm) machine guns and a 75 mm (2.95 in) M4 cannon, then the largest weapon ever carried on an American bomber.

B-25G

The B-25G followed the success of the prototype XB-25G and production was a continuation of the NA96.

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.

The USSR also tested the G (number made: 463; five converted Cs, 58 modified Cs, 400 production).

B-25H

An improved version of the B-25G, this version relocated the manned dorsal turret to a more forward location on the fuselage just aft of the flight deck.

It also featured two additional fixed .50 in (12.7 mm) machine guns in the nose and in the H-5 onward, four in fuselage-mounted pods.

The T13E1 light weight cannon replaced the heavy M4 cannon 75 mm (2.95 in).

Single controls were installed from the factory with navigator in the right seat.

B-25J-NC

Follow-on production at Kansas City, the B-25J could be called a cross between the B-25D and the B-25H.

It had a transparent nose, but many of the delivered aircraft were modified to have a strafer nose (J2).

Most of its 14–18 machine guns were forward-facing for strafing missions, including the two guns of the forward-located dorsal turret.

The RAF received 316 aircraft, which were known as the Mitchell III.

The J series was the last factory series production of the B-25.

CB-25J

Utility transport version

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.

The last VB-25J in active service was retired in May 1960 at the Eglin Air Force Base in Florida.

Trainer variants

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 often with the dorsal turret omitted.

TB-25G

Originally designated AT-24B, trainer modification of B-25G

TB-25C

Originally designated AT-24C, trainer modification of B-25C

TB-25J

Originally designated AT-24D, trainer modification of B-25J, another 600 B-25Js were modified after the war.

TB-25K

Hughes E1 fire-control radar trainer (Hughes)

TB-25L

Hayes pilot-trainer conversion 

TB-25M

Hughes E5 fire-control radar trainer 

TB-25N

Hayes navigator-trainer conversion 

U.S. Navy / U.S. Marine Corps variants

PBJ-1C

Similar to the B-25C for the U.S. Navy, it was often fitted with airborne search radar and used in the anti-submarine role.

PBJ-1D

Similar to the B-25D for the U.S. Navy and U.S. Marine Corps, it differed in having a single .50 in (12.7 mm) machine gun in the tail turret and waist gun positions similar to the B-25H.

Often it was fitted with airborne search radar and used in the antisubmarine role.

PBJ-1G

U.S. Navy/U.S. Marine Corps designation for the B-25G, trials only

PBJ-1H

U.S. Navy/U.S. Marine Corps designation for the B-25H

One PBJ-1H was modified with carrier take-off and landing equipment and successfully tested on the USS Shangri-La, but the Navy did not continue development.

PBJ-1J

U.S. Navy designation for the B-25J, it had improvements in radio and other equipment.

Beside the standard armament package, the Marines often fitted it with 5-inch under wing rockets and search radar for the anti-shipping /anti-submarine role.

The large Tiny Tim rocket-powered warhead was used in 1945.

Specifications

B-25H

Crew

5  

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 take-off 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

&

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.