North American B-25D & J Mitchell

This medium weight bomber is named after General Billy Mitchell. Mitchell was first among the American Military to recognize the true potential of aircraft in attacking warships. Following WW-I he campaigned heavily for the creation of a powerful air force. Around 1930 he put on a demonstration for the War Department in which a dive bomber sank a surplus WW-I battleship.

The Mitchell bomber was the result of the new North American design, model number NA-62, submitted to the USAAC. The USAAC was sufficiently impressed to sign a preliminary contract for 184 aircraft with NAA in September 1939, even though the machine hadn't been flown. The aircraft was given the designation "B-25", and first flew on 19 August 1940, with NAA test pilot Vance Breese at the controls. There never was an XB-25. The B-25 was clearly derived from the NA-40. It had tricycle landing gear; the same twin vertical tailfins; Wright Twin Cyclone engines (the R-2600-9 variant, offering 1,350 horsepower); and defensive armament of three .30 caliber (7.62 mm) machine guns with one each in the nose, waist, and floor, plus a 0.50 caliber (12.7 mm) in the tail position. The tail gunner had to lie flat to fire the tail gun, directing fire through a telescopic sight.

Despite the resemblances, the NA-62 was clearly a new aircraft. The deep and narrow fuselage of the NA-40 was replaced by one not so deep and wider, with pilot and copilot sitting side by side in a cabin, rather than tandem under a greenhouse canopy. The wing roots were fixed to the middle of the fuselage rather than the top. The initial B-25 had wings with a constant dihedral from root to wingtip. This led to serious directional stability problems, however, so with the tenth production B-25, the wings outboard of the engines were set horizontal. All following B-25s had this "gull wing" configuration, and initial production was refitted with the new wing.

The USAAC took delivery of its first B-25 in February 1941. 24 B-25s were built in all, and were used for coastal patrol. The very first B-25 was retained by NAA as a company transport, fitted with five passenger seats and various conveniences. This aircraft was named the WHISKEY EXPRESS, and served through the war until it was lost in a belly landing in early 1945.

The next variant, the "B-25A", was largely similar to the B-25, but featured crew armor protection and self-sealing fuel tanks. These modifications resulted in slightly reduced speed and range. The first B-25A flew on 25 February 1941. 40 B-25As were built, and were also assigned to coastal defense. One B-25A claimed the sinking of a Japanese submarine off the West Coast of the US on 24 December 1941.

The defensive armament of the B-25 was clearly ineffective, and so the "B-25B" featured twin Bendix power turrets, each with two .50 caliber machine guns. One of the turrets was placed on top of the rear fuselage and was manned. The other was a retractable belly turret, positioned just forward of the top turret, and remotely sighted through a periscope. The tail gun was deleted, but the .30 caliber machine gun in the nose was retained. The additional armament resulted in an increase in weight, which further reduced performance, since the engines remained unchanged. The wingspan and length of the aircraft were increased slightly. A total of 120 B-25Bs were delivered, all in 1941, finishing off the original USAAF (the "Air Corps" having become the "Air Force" on 29 June 1941) B-25 production contract. The B-25Bs were delivered in time to be thrown into fighting all over the world. 23 were provided as "Mitchell Mark Is" to the British Royal Air Force (RAF), with these aircraft used for operational training out of the Bahamas. A handful of B-25Bs were provided to the Soviets. 40 were slated to be provided to the Dutch in the Netherlands East Indies, but were diverted for American use.

The B-25B had many deficiencies, but would nonetheless perform one of the most daring and spectacular air raids in history. The Doolittle raid on Tokyo made on April 18, 1942. By the time Jimmy Doolittle's B-25Bs were raising hell over Japan, the next variant of the Mitchell, the "B-25C", was already being produced and delivered in quantity. The first B-25C had flown in November 1941, and the variant was in production by the end of that year. While the B-25C was difficult to distinguish externally from a B-25B, one of the few visible characteristics being a bumper knob under the rear fuselage, it represented a considerable tidying up of the Mitchell design, with many detail changes. On the top of the list were improved Wright Twin Cyclone R-2600-13 engines, each providing 1,700 horsepower and compensating for the "weight creep" that had afflicted the Mitchell. Other changes include an autopilot, increased fuel capacity, provision for underwing racks for external fuel tanks or bombs, stronger wings, a de-icer system, and a cabin heater. The B-25C was about 25 centimeters (10 inches) shorter than the B-25B. A navigator's astrodome was added behind the cockpit from the 383rd B-25C on. Armament was initially the same as the B-25B's, but the nose position was upgraded to one fixed and one flexible .50 caliber machine gun in later production.

The B-25C was built at NAA's Inglewood, California, factory. The USAAF was so pleased with the B-25 and was so desperate for aircraft that NAA began to produce the B-25C, under the designation "B-25D", at their new Kansas City, Missouri, factory. A total of 1,620 B-25Cs and 2,290 B-25Ds were built, and saw service all over the world. The first to go into combat were 48 B-25Cs sent to Australia in March 1942. They were followed by more of the same to fight the Japanese in the South Pacific.

While the B-25C/D was making its mark in the South Pacific, it was also seeing action elsewhere. USAAF Mitchells were shuttled to the CBI (China-Burma-India) theater, and then to China itself. The USAAF 12th Air Force, established to support the Allied landings in North Africa in November 1942, made good use of the Mitchell, and would continue to use variants of the type over the Mediterranean and Italy to the end of the war. The RAF received 367 B-25Cs and 212 B-25Ds, which they designated "Mitchell Mark II". The Mitchell Mark IIs were the first B-25s to see combat with the RAF. They conducted their first raid against the Nazis on 22 January 1943, and continued with attacks on airfields and communications centers in preparation for D-Day. Ironically, although the USAAF found good use for the B-25 in almost all other theaters of war, the only B-25 unit the USAAF employed from England performed coastal patrols.

The Soviets were shipped 182 B-25Cs, with eight of these lost in shipment, and 688 B-25Ds, though records of their service in Soviet hands are sketchy. A small number of B-25C/Ds were supplied to the Canadians and used for training. * The US Marine Corps (USMC) were major operators of the B-25C and B-25D. They obtained 50 B-25Cs as "PBJ-1Cs" and 152 B-25Ds as "PBJ-1Ds". These aircraft often featured a number of significant (and highly variable) differences from their USAAF counterparts. Most visible of these changes was the occasional fit of an APS-3 search radar through the aircraft's front glazing, resulting in a nickname of "hose nose". AN/APS-2 or AN/APS-3 search radar was sometimes fitted as an alternate, with the radome replacing the belly turret. LORAN navigation gear was also fitted.

Additional armament was also provided. Four .50 caliber machine guns were provided in blister packs below the cockpit, and up to three machine guns were fitted in the nose, though these nose guns were often removed. A single tail gun was fitted, with the gunner firing in a prone position. Later production had a raised position for the tail gunner. Waist gun positions were also added to later production, though the top turret was often deleted. The bomb bay was modified to handle mines and depth charges, and an underbelly rack permitted external carriage of a torpedo. When the 5 inch (12.7 centimeter) HVAR (high velocity air rocket) became available, ten stub attachments for these rockets were provided under the wings, giving the PBJ-1 tremendous salvo firepower.

Further weapons enhancements were tried by NAA by designing a B-25 variant fitted with an M-4 75 millimeter cannon, firing out the (shortened) nose on the left side of the aircraft. This massive weapon was almost 10 feet long and weighed over 900 pounds. It was manually loaded through a breech block that opened vertically. The aircraft carried a store of 21 rounds of ammunition, with each round weighing 15 pounds. The big gun was mounted in a moving cradle to absorb recoil.

The initial "XB-25G", modified from a production B-25C, first flew on 22 October 1942. As might be expected, the big gun installation encountered a few difficulties, and it took a little time to work the bugs out. The first production B-25G was delivered to the USAAF in May 1943, and featured twin .50 caliber machine guns in the nose along with the big cannon.

Armament fit of the B-25G was otherwise generally similar to that of the B-25C/D, with top and bottom turrets and no tail guns. The remote-control bottom turret was deleted midway through production, and never came back. The same scheme had been used in early combat versions of the B-17 and B-24 and had been found wanting there as well. The worst problem was that sighting through a periscope tended to make the gunners airsick, and was a tricky task to begin with. Doolittle had found the whole idea ridiculous: "A man could learn to play the fiddle good enough for Carnegie Hall before he could learn to fire that thing." It also tended to get stuck in the down position, leading to unwanted drag, and the periscopic sight often got muddy or cracked during landings.

The B-17 and B-24 quickly converted to the manned Sperry ball turret for belly protection. As the B-25 generally operated at low altitude, belly protection was judged to be low priority, and the turret was simply deleted. This helped reduce weight, which was important as the big M-4 cannon cut into the B-25G's performance. 400 B-25Gs were built by NAA Englewood, plus five more that may have been modified B-25Cs. The Kansas City plant modified 63 B-25Cs to the B-25G specification. Two B-25Gs were provided to the RAF, which assigned them the same Mitchell Mark II designation as their B-25C/D predecessor, and one was provided to the USMC as the "PBJ-1G". The B-25G design really did not match up with the "strafer" field modifications, and was not exactly what the combat crews were after. The next variant, the "B-25H", was more in line with reality.

The B-25H retained the 75 millimeter cannon, though it was a different model, the T13E1 gun. However, the B-25H's forward firing machine gun armament was much more impressive, with four .50 caliber machine guns in the nose and two .50 caliber guns on each side of the cockpit in blister packs, for a total of eight forward-firing machine guns. (The first 300 B-25Hs only had the blister machine guns on the right side of the aircraft.) The B-25H incorporated the Mitchell's first really functional tail turret, fitted with twin .50 caliber machine guns. The rear fuselage was made deeper to accommodate the turret. There was also a single single flexible .50 caliber machine gun on each side of the fuselage, in staggered positions behind the wing.

The top turret was moved forward to behind the cockpit, where it could contribute to the forward firepower in strafing attacks, and was changed to a new NAA "low drag" design. A pair of small bumps were added on the top of the fuselage behind the front turret to keep the top turret from firing into the tail turret. Crew enthusiasm for such "ricochet generators" was not great, and the bumps were often removed in practice. The B-25H could carry 3,200 pounds of bombs, or could be fitted with stub pylons for eight HVARs and a belly rack for a single torpedo. There was no provision for a copilot, and as the B-25 had become thoroughly established as a low-level attacker, there was no bombardier with the bombs targeted by the pilot through an eyeball sight. The first B-25H was modified from a B-25C and flew in May 1943. B-25H production began to arrive at combat units in early 1944. A total of 1,000 B-25Hs were built, all at the NAA Kansas City plant. It does not appear any B-25Hs were supplied to the RAF or the Red Air Force. 248 B-25Hs ended up in USMC hands as "PBJ-1Hs". As with earlier PBJ-1 versions, the Marine aircraft were sometimes fitted with search radar. Production aircraft were delivered with AN/APS-2 or AN/APS-3 radar in a pod on the right wingtip, but in the field the radar was often transplanted to the nose.

In field operations, the big 75 millimeter cannon did not prove as impressive as it looked. With manual loading, it had a low rate of fire, and the trajectory of its shell was much different from that of the bullets from the forward firing machine guns, preventing the machine guns from being used to target the cannon. Salvo-fired HVARs proved a much more effective approach to heavy forward firepower, and while there some B-25 pilots who liked the big gun, it was often removed in the field.

The B-25J was effectively the same as a B-25H, but with no 75 millimeter cannon and a different nose, or rather a pair of alternate noses. The first was a glass nose with one flexible and two fixed .50 caliber machine guns, and the second was a "strafer" nose with eight .50 caliber machine guns. The longer noses resulted in the B-25J returning to the length of the B-25C/D. In principle, the strafer nose could be fitted to earlier B-25 variants in the field. Other changes included reinstatement of the copilot position, giving the B-15J a six-man crew, and uprated P&W R-2600-29 engines.

The first B-25J flew in December 1943. A total of 4,390 were built at a new NAA plant in Kansas City, making the B-25J the most heavily produced of the Mitchells. 255 of these aircraft ended up in USMC hands as "PBJ-1Js", with the traditional confusing radar fits. The RAF acquired 375 B-25Js and gave them the designation of "Mitchell Mark III", though some records indicate 20 of them were passed back to the USAAF in the field. An unknown number of B-25Js were passed on to the Soviets as well, with a total of 870 Mitchells of all types supplied to the USSR. A number of B-25Js were modified as test platforms for the "AN/APQ-7 Eagle Eye" radar, which was fitted as a "wing" under the waist gun positions. The Eagle Eye was a great improvement over earlier airborne radars, and it would prove very useful when fitted to the Boeing B-29 for raids on Japan.

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