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North American B-25 Mitchell / PBJ

naa-b-25j
B-25J

 

Built as a private venture, the NA-40-1 prototype flew in January 1939. The design was then improved as the NA-62, and in September 1939 the USAAC placed its first order.
 

Ordered into production in August 1939 it took just fifty-three weeks after receiving the initial contract before the first prototype took to the air. The prototype of the B-25 was flown for the first time on August 1940. The first of these 184 B-25 Mitchell entered service in 1941.

It and the first few B-25s off the production line had wings with a constant dihedral from the fuselage to the tips. Only after the 10th one were the wings redesigned with the characteristic gull configuration. Its armament included four .30-caliber machine guns, one in the nose and three amidships, and a single .50-caliber gun in the tail. The usual bomb load was 2,000 pounds with a maximum overload of 3,600 pounds. Large scale production began immediately and early models were in service by the time America entered the war in December 1941.

The B-25A was fitted with self-sealing fuel tanks and armor for the pilot. The B replaced the midship and tailguns with electrically operated turrets. Each turret had two .50-caliber machine guns. The lower turret was remote-controlled. The C and D were provided with automatic flight control equipment.

 

The B-25C was the first version of the Mitchell to be mass-produced. Following the completion of the initial B-25, B-25A, and B-25B contracts, a number of contracts were awarded to North American for 1625 B-25Cs to be built at its Inglewood factory. At the same time, an additional contract was issued for 2290 essentially identical B-25Ds, to be built at a new North American plant in Kansas City, Kansas.
 
The first B-25C contract was approved on September 24, 1940 for 863 aircraft under the company designation NA-82. On June 24, 1941, the Netherlands government ordered an additional 162 aircraft under the designation NA-90 which were later built as the B-25C-5. Lend-Lease funds financed contracts signed on January 23, 1942 for 150 NA-94 (B-25C-10) for Britain and 150 NA-93 (B-25C-15) for China. However, these allotments were not followed in the delivery of actual aircraft.
 
The B-25C was outwardly almost identical to the B-25B. It introduced the R-2600-13 Double Cyclone engine with Holley 1685HA carburetors in place of the earlier Bendix Stromberg PD-13E-2 units. The Bendix carburetors were favored because of their easier maintenance, but they required more careful anti-icing procedures. De-icer and anti-icing systems were added, and a Stewart-Warner cabin heater was added in the left wing. A 24-volt electrical system was also added.
 
The armament of the B-25C was the same as that of the B-25B, namely a single 0.30-inch machine gun in the nose, two 0.50-inch machine guns in the dorsal turret, and two 0.50-inch machine guns in a retractable ventral turret. The ventral turret was often removed in the field.
 
The B-25C introduced a new type of tail skid underneath the extreme rear fuselage, a solid unit which replaced the spring-loaded tail skid of earlier versions. This type of tail skid was retained throughout the Mitchell production run.
 
On the earlier B-25s, the exhaust pipe coming out of the back of the engines extended all the way to a position underneath the forward leading edge of the wing. On the B-25C, the exhaust pipes were considerably shortened, and terminated immediately behind the engines.
 
The fuel was carried in four tanks in the inner wing panels, with a total capacity of 670 US gallons. In addition, a 515-gallon tank could be installed in the bomb bay for ferrying purposes, bringing total fuel capacity to 1255 US gallons.
 
Beginning with B-25C serial number 41-12817, a small transparent scanning blister was installed above the navigator's station. At this time, the turrets were changed to Bendix Amplidyne type, and a carbureter air filter was added. Changes were made so that an additional 304 US gallons of fuel could be carried in auxiliary cells in the outer wing panels, for a total of 974 US gallons.
 
The B-25C-1 production block introduced under-wing bomb racks which could accommodate six to eight 100- to 325-pound bombs. In addition, provisions were made for a rack underneath the fuselage capable of carrying a short 22.4-inch torpedo weighing 2000 pounds. If the torpedo was carried, no bombs could be, although a bomb bay fuel tank could be used. The Mitchell was employed only in limited numbers as a torpedo plane against Japanese shipping. However, extensive use was made of the external wing racks, which could carry six to eight bombs of 100-325 pounds in weight.
 
Beginning with the B-25C-5 production block, the 0.30-inch nose gun was removed and replaced by a flexible 0.50-inch machine gun in the extreme nose and a fixed 0.50-inch machine mounted on the starboard side of the nose and firing through a hole cut into the side of the Plexiglas glazing. At the same time, better winterization provision were made.
 
The B-25C-5 production block also introduced a new type of engine exhaust. The B-25B and earlier C versions had a problem with bright spurts of flame being emitted from the exhaust, a dead giveaway during night operations. This problem was so bad that the Mitchell had to be restricted from night operations where enemy aircraft could be expected. In these earlier versions, the exhaust from each cylinder head was gathered by a collector ring, which directed the exhaust to the outside via a single pipe on the side of the nacelle away from the fuselage. Several different exhaust modifications were tried out in an attempt to alleviate this problem. The most effective arrangement was found to be a the replacement of the single exhaust pipe by a set of "finger"-type flame dampening exhaust collectors which ported the exhaust through groups of small rectangular outlets that stuck out underneath the trailing edge of the cowl flaps. These "finger"-type flame dampeners were installed on the production line beginning with the B-25C-5 production block. These were fairly effective flame quenchers, but they suffered considerable cracking and few B-25Cs reached combat zones without the replacement of these finger exhausts by full collector rings or by the later Clayton S-shaped stacks that were introduced on the -15 production block.
 
The B-25C-10 production block introduced an AM remote reading compass, provisions for additional cabin heating, and an improved scanning lens for the sig.
 
Beginning with the B-25C-15 production block, the exhaust collector ring was replaced with Clayton "S"-shaped flame dampening stacks attached to each individual cylinder. Cutouts and fairings were added to the cowling panels where each of the stacks protruded, creating a rather cluttered cowling shape. These protrusions introduced a slight speed penalty, but this was considered an acceptable tradeoff in view of the better flame dampening that was achieved. This feature was provided on all subsequent Mitchells. However, the new exhaust system was not all that popular with Mitchell crews, since it resulted in an increase in cockpit noise as compared to the old arrangement in which collector rings ported the exhaust to the outboard side of the nacelles.
 
At the same time, emergency hydraulic landing gear lowering devices were provided. The fuel capacity consisted of four tanks in the inner wing panels, with a total capacity of 670 US gallons. In addition, a 515-gallon tank could be installed in the bomb bay for ferrying purposes, bringing total fuel capacity to 1255 US gallons. Later versions had additional auxiliary fuel tanks in the outer wing panels. Later versions could also have 125-gallon tanks fitted in side waist positions, a 215-gallon self-sealing fuel tank installed in the bomb bay, and provisions could be made for a droppable 335-gallon metal bomb-bay fuel tank. Armament: Two 0.50-inch machine guns in dorsal turret. Two 0.50-inch machine guns in retractable ventral turret. One 0.30-inch machine gun in flexible mount in the nose. Starting with B-25C-5 the 0.30-inch nose gun was removed and replaced by a flexible 0.50-inch machine gun in the extreme nose and a fixed 0.50-inch machine mounted on the starboard side of the nose and firing through a hole cut into the side of the Plexiglas glazing. Normal bomb load was 3000 pounds but could be increased on the B-25C-1-NA with external underwing racks to a maximum of 5200 pounds.
Deliveries on a new contract (NA-96) began in February 1943 with the similar B-25C-20.
 
Beginning with production block B-25C-25, a "clear-vision" windshield was installed. Provisions were made for the fitting of additional fuel tanks for ferrying purposes. 125 gallons of fuel could be carried in side-mounted tanks in the waist position. A 215-gallon self-sealing fuel tank could be installed in the bomb bay, and provisions for a droppable 335-gallon metal bomb-bay fuel tank were made on every second airplane.
 
B-25C serial number 43-32732 was fitted with a special bomb bay rack to carry an airborne flame thrower. The results of tests with this unusual feature are unknown.
 
The first B-25C was accepted in December of 1941, with the 1619th and last one being delivered in May of 1943.
 

 

The E and F were fitted with experimental deicing equipment. The G was the first model to carry a 70mm cannon. The H increased its armament to four .50-caliber guns in an armored nose and two pairs of .50-caliber guns on each side of the fuselage. It was the precision bomber version of the H; the crew increased to six to include a bombardier.

The B-25J, built at the Kansas plant, was the most widely produced version, 4318 being produced 1943-45.

The US Marine Corp operated B-25s as the PBJ-1C, D, G, H, and J models.

More than 700 B-25s were acquired by the U.S. Navy and Marines, as the PBJ. The Royal Air Force received about 800, and the airplane was flown more than a dozen other countries. Top speed only reached about 270 mph but the Mitchell's 1,350-mile range made it very useful.

The Americans did not use Mitchells operationally from the United Kingdom but based them with the 12th United States Army Air Force in the Mediterranean. However the British, Dutch and Russians received large numbers.

Training aircraft were the AT-25, later designated the TB-25.

All B-25 models were powered by Wright R-2600 Cyclone 14 engine. More than 12000 aircraft built.

In April 1942 sixteen Mitchells, operating from the American aircraft carrier USS Hornet, made one of the most daring bomber raids in the Second World War, on Tokyo.

 

b25-fac
 
In 1955 large numbers of these wartime medium bombers were still used by the R.C.A.F. for a variety of duties. The target towing version shown here is powered by two 1,700 h.p. Wright R2600-13 engines.
 
  NA-B25D
B-25D
 
About 100 B-25Js, with glazed noses, are used for all weather crew training and guided weapon development. Other B-25Ds and Js were used by Reserve squadrons. TB-25s were in service with the U.S.A.F.
 
The Mitchell was used in all theaters and a total of 9816 were built, essentially unaltered in airframe and powerplants, but revised in armament, armour and fuel. There were 1619 B-25C built, and 1000 B-25J.

 

Serials of North American B-25C Mitchell
B-25C
41-12434-13038 / c/n 82-5069/82-5673
B-25C-1
41-13039-13296 / c/n 82-5674/82-5931
B-25C-10
42-32233-32382 / c/n 94-12641/94-12790
B-25C-15
42-32383-32532 / c/n 93-12491/93-12640
B-25C-5
42-53332-53493 / c/n 90-11819/90-11980
B-25C-20
42-64502-64701 / c/n 96-16381/96-16580
B-25C-25
42-64702-64801 / c/n 96-16581/96-16680  

 

Gallery

 

B-25
Initial model
 
B-25B
Dorsal & ventral turrets
 
B-25C Mitchell:
Engines: Two Wright R-2600-13 Double Cyclone, 1700 hp takeoff, 1500 hp at 2400 rpm.
Wingspan: 67 ft 67.7 in
Length: 53 ft 0 in
Height: 15 ft 9 in
Wing area: 610 sq.ft
Empty weight: 20,300 lb
Maximum weight: 34,000 lb
Maximum speed: 284 mph at 15,000 ft.
Cruising speed: 233 mph at 15,000 ft.
Initial climb rate: 1100 fpm
Time to 15,000 ft: 16.5 min
Service ceiling: 24,000 ft
Range: 1500 miles with 3000 lb bombs.
Internal fuel capacity: 670 US gal
Ferry fuel capacity: 1255 US gal
Opt fuel later mods: 800 US gal
Armament B-25C: 4 x 0.50-inch machine guns, 1 x 0.30-inch machine gun
Armament B-25C-5: 6 x 0.50-inch machine guns
Normal bomb load: 3000 lb
Underwing bomb load B-25C-1-NA: 2200 lb

Max bomb load B-25C-1-NA: 5200 lb

 
B-25D Mitchell
Ventral bomb racks
Engines: two 1,700 h.p. Wright R2600-13
Span: 67 ft. 7 in
Max Weight: 33,500 lb
Max Speed: 303 m.p.h.
 
B-25G
Heavy nose gun
 
B-25H
Improved B-25G
Engines: Wright R-2600-13 Cyclone, 1700 hp / 1268 kW
Wingspan: 67 ft 7 in / 20.60 m
Length: 51 ft 0 in / 13.34 m
Height: 15 ft 9 in / 4.80 m
Wing area: 610,0 sq.ft / 56.67 sq.m
Empty weight: 19,975 lb / 9061 kg
MTOW: 36,047 lb / 16,351 kg
Max speed: 275 mph / 442 kph at 13,000 ft / 3960 m
Climb to 15,000 ft / 4570 m: 19 min 0 sec
Service ceiling: 23,800 ft / 7255 m
Range: 2700 m / 4344 km
Armament: 1 x 75mm M4 cannon, 12 x .50 in mg
Bomb load: 3200 lb / 1452 kg or 1 x 2000 lb / 907 kg torpedo
Seats: 5
 
B-25J
Improved B-25H initially with B-25D glazed nose, later solid 8 gun nose
Engines: 2 x Wright R-2600-92 Cyclone, 1268kW / 1700 hp
Max take-off weight: 15876 kg / 35001 lb
Empty weight: 8836 kg / 19480 lb
Wingspan: 20.6 m / 67 ft 7 in
Length: 16.13 m / 52 ft 11 in
Height: 4.98 m / 16 ft 4 in
Wing area: 56.67 sq.m / 609.99 sq ft
Max. speed: 237 kts /438 km/h / 272 mph
Cruising speed: 200 kts / 370 km/h
Ceiling: 7375 m / 24200 ft
Cruising altitude: 12992 ft / 3960 m
Wing load: 57.4 lb/sq.ft / 280.0 kg/sq.m
Range: 2173 km / 1350 miles
Armament: 12 x 12.7mm / .50 machine-guns, 1300-1800kg of bombs
Crew: 5
 
TB-25
 
PBJ‑1D Mitchell
 
PBJ‑1H

 

na-b-25-ld

North American B-25 Mitchell

 

 


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