B-25 Mitchell – The Aircraft Carrier based Bomber
The North American B-25 Mitchell is one of the most iconic combat aircraft of the Second World War, and the original symbol of US defiance during the early stages of that conflict.
Originally conceived as a fast medium bomber, the B-25 served in a bewildering variety of roles during the war and gained special fame in the South West Pacific Area for its prowess as a low-level raider and strike aircraft against both surface and maritime targets.
In combat use for almost the entirety of the Second World War, the B-25 served with many Allied air forces but the majority of those manufactured saw action with the USAAC/USAAF.
Design and Development
The B-25 was named for Brigadier General William ‘Billy’ Mitchell, an airpower theorist and innovator whose brilliance as a radical free-thinker was not enough to stop his eventual court-martial, and resignation from the service.
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In 1939 the USAAC issued a requirement for a fast medium bomber that could carry a bombload of 2,500 lbs (1,100 kg) over distances of 1,200 miles (1,900 km) and at a speed of 300 mph (430 km/h).
North American Aviation offered the NA-62 design, which was accepted and put into service at the B-25. Problems with the profile of the main wing saw some re-design work, and the improved B-25A entered service in 1940, swiftly followed by the B-25B version.
Constant improvements in the design saw the introduction of the B-25C, the first mass-produced version. With improved engines and re-designed gunner stations, the ‘C’ variant saw widespread service with the USAAF and was also exported to Allied nations such as the UK and the USSR.
The B-25D was basically a ‘C’ model with multiple small improvements, and continued the original design concept by having a plexiglass nose like earlier models, being optimised for the mid-level bombing.
But the next variant was a radical departure from the stated intention of medium bombing and marked the start of the B-25 being employed as a low-level raider. In the B-25G, the transparent nose was replaced with a shortened solid front section holding several .50 calibre machine guns, and an M4 75mm (2.75 inch) cannon, making it the most heavily-armed aircraft of the war to date.
The B-25H was an improved version of the ‘G; model, with a relocated upper turret, added 6 .50 calibre machine guns to the forward-firing strafing battery, and introduced the lightweight T13E1 75 mm cannon to replace the heavier M4. This was the most heavily armed version of the B-25 and became the bane of Japanese troops and naval ships in the SWPA.
The last production version of the Mitchell was the B-25J, which re-introduced the transparent nose for the medium bombing, but half of the production run of this variant was manufactured as low-level attack aircraft, with the solid strafer nose and cannon fitted instead.
The crew of a B-25 consisted of 5-6 personnel: pilot, flight engineer/co-pilot (later models), navigator/bombardier, turret gunner, waist gunner and a tail gunner.
The B-25 had the following dimension: a height of 16 ft. 4 inches (5 metres), a length of 53 feet (16 metres) and a wingspan of 67 feet (20 metres). Empty, the B-25 weighed in at 19,500 lbs (8,800 kg) and the Maximum Take-off Weight was 35,000 lbs (16,000 kg).
The Mitchell had internal tankage for 974 gallons of fuel, giving a range of 1,350 miles (2,200 km) but this could be extended to over 3,000 km with the use of drop tanks under the wings. The aircraft was powered by two Wright R2600-92 Twin Cyclone 14-cylinder radial engines, each producing 1,700hp, but could be boosted during emergencies to 1,825hp when required.
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These power plants gave the B-25 a top speed of 275 mph (440 km/h) and a nominal cruising speed of 230 mph (370 km/h). The service ceiling of the B-25 was 24,000 feet (7,400 metres).
The B-25 was a very heavily armed aircraft, especially the later marks which were optimised for a low-level strikes. The aircraft could carry up to 14 M2 .50 calibre machine guns, and eight of these formed the battery pack in the nose and forward fuselage of later variants, making the Mitchell a devastating aircraft when used to strafe ground and naval targets.
In addition, the 75mm cannon enabled the Mitchell to engage nearly any type of surface target with high-explosive shells, as well as a blizzard of fire from the forward-facing machine gun battery.
The Mitchell could carry 3,000 lbs (1,400 kg) of bombs internally and had external racks under the wings for carrying eight HVAR ground-attack rockets. A ventral shackle mount could be used to carry and employ a Mark 13 torpedo.
Mitchells were also used in mining operations and were also known for carrying depth charges on the wing racks for ASW use. In all, the B-25 was one of the most versatile aircraft used by the Allies, and also had a reputation for being one of the most heavily armed aircraft used in combat during the Second World War.
The B-25 served valiantly from the commencement of the Pacific War and was the first platform to be used offensively by the USAAF against the Japanese homeland.
After the shock of the Pearl Harbour raid, the Americans were determined to strike back swiftly in any way possible, to send a message to the Japanese government about the seriousness of American intentions to take the war to the enemy.
Accordingly, 16 B-25B’s were loaded onto the carrier USS Hornet, and accompanied by the USS Enterprise and supporting fleet proceeded to approach the Japanese mainland with the intention of performing a surprise bombing attack.
These B-25Bs were heavily modified for the mission, with most of the defensive weapons removed to save weight, extra fuel tanks fitted to increase range and autopilots installed to further help with the long-range strike.
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As the aircraft were unable to recover aboard the Hornet, the directions from Lt-Col Jimmy Doolittle as raid commander were for all aircraft to continue onto China after dropping their bombloads over Japan, hopefully landing on improvised airfields but baling out over friendly territory as a last resort.
With all aircraft launched 500 km from the Japanese coast, history records the Doolittle Raid as a great success, with little material damage being suffered but Japanese confidence receiving a severe shock, and this attack convinced the Japanese military government to retain combat aircraft for home protection duties, a decision that considerably weakened Japanese military aviation in other more active theatres.
The British and Americans used the Mitchell in North Africa, Italy and the Mediterranean operational areas. B-25s were employed as strike aircraft in North Africa, attacking ground targets and also making life miserable for merchant shipping trying to re-supply Axis forces in the area.
In Sicily, the aircraft was chosen for many medium bombing raids ranging far into Italy, as the B-25 had a longer range than the A-20 Havoc and the A-26 Invader.
After the Normandy invasion in June 1944, the RAF and the Free French air force used the Mitchell in medium bombing raids against the continent, and also as air support for Allied forces advancing through France. The USAAF did not employ the B-25 in the European Theatre of Operations.
It was in the Pacific War, and most specifically in the South-West Pacific Area (SWPA) that the Mitchell came into its own as a low-level raider. With lush jungle canopies shielding Japanese forces from view, it was found that medium-level bombing was not as effective as when applied in different theatres such as North Africa.
This led to the widespread employment of cannon-and-machine gun-armed B-25s as low-level raiders, at altitudes that exposed Japanese forces to observation and attack from the air.
Japanese merchant shipping and naval forces were also extremely vulnerable to air strikes from heavily armed aircraft, and the B-25 was recorded to have caused very heavy losses in all types of Japanese vessels, whether merchant or naval.
The Battle of the Bismarck Sea in 1943 was the best example of the carnage suffered by the Imperial Japanese Navy during this time. A Japanese convoy of eight troop transports escorted by eight destroyers was attacked by Allied air forces while attempting to reinforce Japanese forces at Lae.
Led by USAAF Mitchells and RAAF Beaufighters, the convoy was under unrelenting aerial assault for three days and nights in March of that year, and the B-25 pilots were noted for their employment of ‘skip’ bombing attacks from masthead height with devastating results.
All of the transports and four of the destroyers were sunk, and over 3,000 Japanese soldiers and sailors were killed before the operation was called off, and the few survivors returned to Rabaul.
B-25s were employed by the Allies for the remainder of the Pacific War, greatly helping the advance to the Philippines, and providing much air support for Allied troops as they slowly advanced towards the Japanese mainland.
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Japanese ground forces learned to hate the B-25 for its horrific firepower and determination in pressing its ground attacks, and the effects of up to ten forward-firing .50 calibre machine guns in strafing run – along with a hail of 75 mm High Explosive shells – must have been terrifying to the targets of such attacks.
The B-25 served with distinction in many Allied air forces during the war, including the Russian, Free French, Australian, Canadian and the Royal Air Force. After the cessation of fighting in late 1945 the USAAF employed the B-25 as a high-speed transport for a few years, but most air forces retired all their Mitchells soon after the end of the war, but the type served on with many smaller air forces for some considerable time after 1945. The Last B-25 in military service was retired by the Indonesian air force in 1979.
If the B-25 wasn’t a war-winning weapon, it was definitely a war-saving one. The Allies were extremely lucky to have such a superb medium bomber from the start of the war, but the B-25 really hit its straps after the platform’s ability as a low-level raider was realised.
It is a well-remembered and loved combat aircraft of the Second World War with a sterling service record, but has also gained a large degree of immortality by its employment in the Doolittle Raid, giving a massive boost to Allied morale when things were looking increasingly desperate in the early stages of the Pacific War.
The last word can be left to FDR Roosevelt who ordered the first aerial attack on Japan. When asked from where the raiding B-25s had come from, the President laughingly answered: “Shangri-La!”
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- 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)
- 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
- 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)