v1.0.1 / 01 apr 02 / greg goebel / public domain
* North American Aviation contributed three great aircraft to the Allied cause during World War II: the "AT-6 Texan" trainer, the "P-51 Mustang" fighter, and the "B-25 Mitchell" medium bomber. While the Mustang is clearly the most famous of the three, the Mitchell was likely the most important aircraft in its own class, built in large quantity and proving its worth in both the Pacific and European theaters of war.
In particular, the Mitchell gave America one of its first victories during the dark days of early 1942, when Jimmy Doolittle's raiders swept over Japan to humiliate the enemy. This document provides a short history of the Mitchell.
* In the years leading up to World War II, the North American Aviation (NAA) company of Inglewood, California, led by President James H. "Dutch" Kindelberger, developed new aircraft to help meet the demands of the US military as they prepared for war.
In 1936, in response to a US Army Air Corps (USAAC) competition for a new medium bomber, NAA developed a twin-engine "tailsitter" aircraft designated the "NA-21", with the aircraft's first flight on 22 December 1936.
The NA-21 was not a very impressive aircraft, with the appearance of a civilian transport, but it was NAA's first multi-engined aircraft. The NA-21 had a bigger bomb load than a B-17, and although its defensive armament was light, consisting of five 7.62 millimeter (0.30 caliber) machine guns, it had the first hydraulically-operated gun turret to be used on a USAAC aircraft. The turret was designed by Edgar Schmued of NAA, a German immigrant who would play a vital part in the development of the P-51.
Unfortunately, the NA-21 weighed over 18 tonnes (40,000 pounds), while its twin 14-cylinder Pratt & Whitney (P&W) R-1830 Twin Wasp two-row radial engines only provided 800 horsepower each, making the aircraft seriously underpowered. The NA-21 was flown to the USAAC test facility at Wright Field, Ohio, in March 1937, for competitive evaluation.
The NA-21 lost the competition to the Douglas "B-18 Bolo", largely because Douglas was only asking half as much for the B-18 as NAA wanted for the NA-21. However, the USAAC decided to purchase the NA-21 prototype anyway.
The aircraft went back to California, where it was rebuilt and refitted with turbosupercharged 14-cylinder P&W R-2180 Twin Hornet two-row radials, providing a maximum of 1,250 horsepower at medium altitude. The aircraft, now with the company designation of NA-39 and military designation of "XB-21 Dragon", flew back to Wright Field in early 1939. NAA proposed to sell a batch of Dragons to the USAAC, but the price was still too high. The XB-21 was flight-tested at Wright Field for several more years.
* The NA-21 was not a promising start for NAA in the bomber business, but the company's engineers knew they were taking baby steps and could do better. In fact, they were already working on what they believed would be an improved bomber aircraft, the "NA-40", for a USAAC requirement issued in 1938.
The NA-40 first took to the air on 29 January 1939 and didn't prove to be quite the step forward envisioned. The NA-40 at least looked more modern than the NA-21. It had a long narrow fuselage, with the pilot and copilot sitting in tandem, rather than side-by-side, in a greenhouse-style canopy; a solid nose; and high mounted wings, each carrying a 1,100 horsepower Pratt & Whitney R-1830-563CG Twin Wasp radial engine.
The NA-40 had tricycle landing gear, and a wide horizontal tailplane capped by vertical tailplanes at the end. Defensive armament consisted only of three 7.62 millimeter machine guns: one in the nose, one that could be moved around the belly or waist position, and one in a rear dorsal turret.
Flight tests proved the NA-40 left very much to be desired. The NA-40 suffered from severe vibration, and the top speed was only 425 KPH (265 MPH). After only a little more than five hours in the air, the NA-40 went back to the factory for rework.
* The updated "NA-40B" first flew on 1 March 1939, and featured twin 1,600 horsepower 14-cylinder Wright R-2600-A71-3 two-row Twin Cyclone radials; a glazed nose; and many aerodynamic changes. Flight tests showed that the new design did much to eliminate the vibration problems, and that top speed had increased by 32 KPH (20 MPH).
The NA-40B was flown to Wright Field for USAAC evaluation, but on 11 April 1939 the aircraft lost one engine and spun into the ground. The crew managed to get out unharmed, but the NA-40B caught fire and was destroyed. NAA didn't get a production contract. The company's engineers went back to the drawing board to think things over again.
* Their incentive was yet another USAAC requirement for a medium bomber, this one having been issued in March 1939, even before the crash of the NA-40B. The USAAC wanted a bomber that had a range of 3,200 kilometers (2,000 miles), a maximum speed of 480 KPH (300 MPH), and a bomb load of 1,360 kilograms (3,000 pounds).
The result was the "NA-62". The USAAC was sufficiently impressed with the design 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 7.62 millimeter guns with one each in the nose, waist, and floor, plus a 12.7 millimeter (0.50 caliber) 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 prototype's vertical tailplanes were in the shape of rounded-off rectangles, but NAA engineers experimented with five more shapes until settling on a more satisfactory configuration with an angled leading edge. The end result of such tweaking was an aircraft with excellent handling characteristics, despite its relatively high performance.
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.
Following a suggestion by NAA's Lee Atwood, the USAAC formally assigned the type the name of "Mitchell", in honor of General Billy Mitchell, who had pioneered concepts of air power in the 1920s. 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 12.7 millimeter 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 7.62 millimeter 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.
For months after the Japanese attack on the US Navy base at Pearl Harbor on 7 December 1941, the Americans were staggered by a string of disastrous defeats. The US was poorly prepared for war, had been distracted by the fighting in Europe, and had generally dismissed Japanese military capabilities.
The resources weren't yet available to seriously turn the battle against the Japanese, but the humiliated Americans were desperate to prove they could fight back. A strike on Japan using conventional carrier-based aircraft was out of the question. The US had only a few precious carriers to counter Japanese naval thrusts, and the Japanese would be delighted if the Americans were so foolish as to bring their carriers close to Japan, where they would certainly be sunk by superior Japanese air and naval power.
The USAAF did not have bombers that had the range to reach distant Japan from any available land bases. However, on 10 January 1942, a month after Pearl Harbor, a US Navy captain named Francis S. Low was flying to inspect the new carrier HORNET, when he saw Army bombers perform simulated bomb runs over the outline of a carrier deck painted on a runway.
He realized that a collaboration between the US Navy and the USAAF might do the trick. Low, who was on the staff of Admiral Ernest J. King, immediately went to King to suggest that relatively long-range Army bombers be launched off a carrier to attack Japan.
King had another of his staff officers, Captain Donald B. Duncan, perform some "back of the envelope" calculations that showed the idea was feasible. King contacted General Henry H. "Hap" Arnold, commander of the USAAF, to promote the idea. Arnold was agreeable, and assigned implementation of the plan to Lieutenant Colonel Jimmy Doolittle, one of his own staff officers. The plan was given the cover name of the "First Aviation Project".
Jimmy Doolittle had built a reputation before the war as a stunt flyer, air racer, and pioneer in aviation technology. He had all the skills and competence to put together such a mission, but Arnold did not intend for Doolittle participate in the actual raid. Doolittle was too valuable to risk and, at age 45, was regarded as too old for a difficult combat mission.
* Doolittle considered the bombers available to the USAAF, and found the Mitchell the best suited to the job. 24 B-25Bs were modified at the Northwest Orient Air Lines center in Saint Paul, Minnesota for the mission. Armor was removed; the remote control lower turret, which nobody found particularly useful, was replaced by a 190 liter (50 US gallon) fuel tank. Other fuel tanks were added, increasing the capacity of the B-25B to a total of 4,320 liters (1,140 US gallons) from a normal capacity of 2,625 liters (694 US gallons).
Painted broomstick handles were fitted in the tail as dummy guns. As the raid was to be at low level, the top-secret Norden bombsight was removed and replaced with a simple post-and-notch sight made from a few pieces of metal. The reduced armament allowed the crew to be cut from 7 to 5 men, further cutting weight, as well as manpower requirements and the number of crewmen at risk.
Doolittle had calculated that the weight reductions would be enough to get the B-25s off the carrier deck safely, but he was enough of an engineer to know that theory and practice were two different things. While the new carrier HORNET was on her shakedown run off of Norfolk, Virginia, in February 1942, a pair of B-25s took off from her flight deck without incident. It could be done.
Volunteers were selected from the coastal patrol B-25 crews for an unspecified dangerous mission. In early March 1942, they arrived at Eglin Field in Florida for three weeks of specialized training. There they met Doolittle, who told them nothing more about their mission and emphasized that it would be risky. He told them if anyone wanted to pull out, they were free to do so without recriminations. None did.
The crews were trained by Navy Lieutenant Henry L. Miller to make takeoffs in less than 230 meters (750 feet) by hauling back on the control column and pulling up in a steep near-stall climb. The pilots learned the procedure quickly and became adept at it, although two of the aircraft were lost without casualties in crackups. They also practiced low-level bombing runs using the new sight, with the bombers coming in very low and then pulling up over the target to release ordnance at about 450 meters (1,500 feet).
The flight crews were given a wide range of vaccinations for tropical diseases, but Doolittle discouraged them from speculating on the nature of their mission, even with their wives.
* In mid-March, Doolittle went back to Washington to brief Hap Arnold on the progress of the First Aviation Project. During the briefing, Doolittle asked Arnold: "I'd like your permission to lead this mission myself."
Arnold turned him down, but Doolittle was stubborn and persistent, and Arnold finally told him that if the Air Corps' chief of staff, Major General Millard F. Harmon, gave his consent then Doolittle could lead the raid.
Doolittle knew that Arnold would call Harmon and order him to turn Doolittle down, so the instant Doolittle left Arnold's office he took off at a sprint over to Harmon's office. Stretching the truth a bit, Doolittle told Harmon that he had spoken with Arnold about leading the Tokyo raid, and Arnold had said that if it were OK with Harmon it was OK with him. "Sure, Jimmy, it's all yours," Harmon replied.
Doolittle left the office, heard the phone ring, and overheard Harmon saying something about not wanting to go back on his word. Doolittle returned to Eglin with the expectation of being ordered to stay behind, but it never happened.
* At the end of the month, the aircraft and crews flew to Sacramento, California, where they given further modifications at McClellan Army Air Base, and then on to Alameda Naval Air Station in the San Francisco Bay area. On 1 April 1942, 16 B-25s were loaded onto the carrier HORNET and lashed down to the deck. The next day, the HORNET steamed out to sea under the Golden Gate bridge.
The ship's captain, Marc A. Mitscher, finally revealed their destination: "This force is bound for Tokyo!" The crew cheered. The bombers were kept clean of any evidence that they had been on the HORNET to ensure secrecy if any were to fall into Japanese hands.
The weather was poor and seas was rough. On Monday, 13 April, the HORNET was joined by the carrier ENTERPRISE, as well as four cruisers, eight destroyers, and two oilers. The group was designated Task Force 16 and was under the command of Admiral William F. Halsey, on board the ENTERPRISE.
The B-25s were set up in takeoff positions on 16 April, preparatory to the planned launch on 19 April from a position 725 kilometers (450 miles) east of Tokyo. The first aircraft to take off had the least runway. Doolittle's was first, with only 142 meters (467 feet) for takeoff, but the HORNET would steam into the wind for takeoff, and hopefully that would be enough runway to get the aircraft into the air.
Unfortunately, on the morning of 18 April, Task Force 16 ran into a Japanese fishing boat that was operating as a radio picket. The boat was promptly sunk, but not before it managed to broadcast a report back to its base, and communications intercepts clearly showed that the Japanese were alerted that something going on.
Task Force 16 was still 1,050 kilometers (650 miles) from Tokyo, but Halsey could not risk his carriers. He ordered: LAUNCH PLANES. TO COLONEL DOOLITTLE AND GALLANT COMMAND, GOOD LUCK AND GOD BLESS YOU.
Doolittle loaded up his B-25s with 190 liters (50 US gallons) of extra fuel, and the planes were rocked back and forth to ensure that the tanks were as full as could be. Additional fuel was carried in gas cans, to be used to top off the tanks. However, even with the bigger fuel load, the range of his bombers would be stretched to the limit.
At 0820 on 18 April 1942, the HORNET's flight deck officer, Navy Lieutenant Edgar G. Osborne, flagged Doolittle to take off. The weather was still rough, but a gale wind of 75 KPH (40 knots) actually made takeoff easier. The B-25 made it off the carrier with 30 meters (100 feet) to spare.
If any Mitchell couldn't take off, the crews had been instructed to leave the aircraft immediately so it could be thrown over the side of the carrier to let the others go. Fortunately, all 15 other bombers followed over the next hour, all making it safely into the air though a few skimmed the waves before they managed to make altitude. The only trouble occurred when a seaman was blown by the wind into a propeller that mangled his left arm.
* After a flight of four hours, Doolittle roared in over Tokyo and dumped his bombs on a factory complex. Eight other B-25s following him hit Tokyo, with the remainder hitting industrial targets in Yokohama, Nagoya, and Kobe.
Japanese air defenses were bewildered and none of the aircraft were shot down. One even flew through the landing pattern of an airfield and was not attacked. Only one was hit by flak, and it was not seriously damaged. However, head winds slowed their progress towards China, and the fact that they had been forced to take off in the morning meant flying into China at night.
One of the raiders flew into Soviet territory north of Vladivostok and landed. The Soviets were not at war with Japan, were too busy fighting Hitler to want to provoke the Japanese for the time being, and when they had been asked earlier to allow the B-25s to land in their territory, they had refused. The crew was interned even though the US and the USSR were allies. The fliers were allowed to "escape" into Iran 14 months later. Their B-25B was never returned, and there are hints that it may be still in existence somewhere in the former Soviet Union.
The landing areas in China were socked in by bad weather, and so eleven of the crews baled out, mostly near the Chinese city of Chuchow. Of these 55 men, one was killed by a bad parachute landing, while one crew was captured by the Japanese. Of these five, the Japanese executed two, while the other three remained prisoners for the rest of the war.
Four planes crash-landed. Two did so without injury to their crews. One came down near the China coast, with four of its crew seriously injured, though they were helped by the Chinese to safety. The other lost two men killed in the crash landing, with the three others captured by the Japanese. The pilot was executed, the copilot died in captivity of malnutrition, and only one of this crew survived the war.
Considering the risky nature of the raid and the hasty launch of the aircraft from extended range, the losses in personnel were surprisingly light. When the Sun came up on 19 April, Doolittle tried to round up his men. He told one of his men that he feared he would be court-martialed for losing his aircraft. The flier said they would give him a medal instead, and in fact he was awarded the Medal of Honor instead and was promoted to brigadier general. He would go on to be a senior USAAF bomber commander in Europe.
* The Doolittle raid was the first real success enjoyed by the Americans in the war against the Japanese. President Roosevelt announced the raid to the public, reporting the planes had flown from a secret base in the land of "Shangri-La". The operation was worth every aircraft lost in the boost to civilian and military morale.
The Japanese high command was humiliated. While the "Do-Little" raid had caused no real damage, the Japanese military had been taken completely by surprise, and worse yet, American bombers had overflown the grounds of the Imperial Palace in Tokyo. Failure to prevent a threat to the Emperor was a serious disgrace.
Precious military resources needed to maintain the momentum of the offensive against the Americans were diverted to home defense, and Admiral Isoroku Yamamoto, the brilliant Japanese strategist who had devised the attack on Pearl Harbor, put into motion a plan to lure the American carriers into battle, destroy them, and eliminate the American threat once and for all.
The result was the Battle of Midway in June 1942, where the Japanese Imperial Navy suffered a disastrous defeat at the hands of an inferior US Navy force that put a stop to Japanese expansion in the Pacific and badly injured Japanese naval air power.
* 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.
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 12.7 millimeter 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. They would be put to very ingenious use by a pair of clever aggressive USAAF officers.
Major General George C. Kenney was a tough little guy who had been a fighter pilot in World War I, and was put in charge of the 5th Air Force under General Douglas MacArthur in August 1942. MacArthur was an imperious and domineering SOB who demanded subordination from his officers, but although Kenney had little fear of speaking his mind, his skills were such that MacArthur grudgingly tolerated the back-talk.
Kenney acquired a useful subordinate of his own, in the form of Colonel Paul I. "Pappy" Gunn. Gunn had enlisted in the Navy in World War I. He had wanted to fly, but the Navy turned him down, and he left the service to learn how to fly on his own initiative. He managed to get Navy wings when he reenlisted in 1925. He had retired from the Navy as a chief petty officer in 1937.
Gunn was working for the Philippine Air Lines in Manila as their maintenance chief when war broke out. When the Japanese attacked the Philippines, he was sworn into the US Army as a captain, and did what he could to support the futile American defense of the islands. When the Philippines were overrun, he escaped to Australia in a Beechcraft and presently found himself working for Kenney.
Kenney had a tooth-and-claw instinct in air warfare. To Kenney, as he said in a report to Hap Arnold, air superiority meant "air control so supreme that the birds have to wear Air Force insignia." Kenney was particularly fond of low-level strike tactics for attacks on both land and sea targets.
He devised methods for attacking Japanese airfields in New Guinea and other South Pacific islands with Douglas A-20 Boston medium bombers. A first wave of A-20s, modified by Gunn to carry four additional fixed 12.7 millimeter machine guns in the nose, would sweep in over the target to disrupt defenses. It would then be followed by a second wave, dropping ten kilogram (23 pound) parachute-retarded "parafrag" bombs to shred the airfield, as well as white-phosphorus incendiary bombs to burn whatever was left.
Japanese propaganda blasted Kenney's "new and fiendish methods of warfare" and called the Americans "gangsters". Undoubtedly, this was received as a compliment. Kenney applied a similar approach to antishipping strikes using the B-25. Gunn, working with NAA field representative Jack Fox at the Townsville Air Depot in Queensland, Australia, modified B-25Cs and B-25Ds to accommodate a typical fit of four 12.7 millimeter machine guns in the nose and two or four such weapons in blister packages below the cockpit.
While prewar US air combat doctrine emphasized medium or high altitude bombing attacks on shipping, experience had shown this approach to be ineffective. Kenney's aircrews instead developed a new scheme known as "skip bombing", in which a B-25 came in low over the water, spraying the target with its nose guns to wipe out enemy gunners, and then released a bomb with a time-delay fuze to skip over the water and slam into the target, exploding after the bomber had made its getaway.
Skip-bombing was dangerous, since the attacker had to fly into the teeth of a ship's flak at such low level that there were cases of bombers striking the ship's mast. The bomb could even skip back up and hit the bomber. However, skip bombing was also murderously effective.
* This was proven in early March 1943, when the Japanese attempted to ship 7,000 troops in a convoy from their major base at Rabaul in New Britain to Lae in New Guinea. The Japanese did not have air superiority, but they hoped bad weather would protect the convoy, which consisted of about eight transports and eight destroyers.
The convoy was spotted on 1 March, and was attacked by B-17s the next day. The Fortresses claimed several hits. On 3 March, the convoy was attacked by everything the Allies had: Fortresses, Bristol Beaufighters, and skip-bombing A-20s and B-25s. The result was a massacre, with ships blasted and sunk while the attackers mercilessly strafed the survivors in the water.
All eight transports and four destroyers were sunk, and only about 800 Japanese soldiers made it to Lae. More than 3,600 were killed, at a loss to the Allies of 13 dead and 12 wounded. The survivors were ferried back to Rabaul on surviving destroyers. The "Battle of the Bismarck Sea", as it would be known, was a dramatic demonstration of air power.
Such actions were repeated. On 2 November 1943, the USAAF hit the heavily defended Rabaul harbor with four squadrons of B-25s, escorted by Lockheed P-38 Lightning fighters. Of the 38 warships and 20 merchantmen in the harbor, 30 were hit. Japanese fighters came up in force and Kenney lost 20 aircraft, but 60 of the defenders were shot down in a wild mass dogfight with the P-38s.
* 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 12.7 millimeter 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 12.7 centimeter (5 inch) 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.
* The B-25C/D led to a pair of one-shot experiment variants, the "XB-25E" and the "XB-25F", both of which were modified B-25Cs used to test prototype de-icing systems. Pictures that survive of the sole XB-25E show it to have a distinctive engine cowling scheme. Few details survive concerning the XB-25F.
* Even while Pappy Gunn was hacking up B-25s in the field to increase their forward firepower, NAA engineers were considering their own firepower enhancements 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 three meters (9 feet 6 inches) long and weighed over 400 kilograms (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 6.8 kilograms (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 12.7 millimeter machine guns in the nose along with the big cannon.
There was a push to provide even more firepower, with an experiment conducted with a B-25C to fit it with a belly tray with twin 37 millimeter cannon and a small bombbay for parafrags. The shock of firing was too much for the airframe and this scheme was abandoned.
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 12.7 millimeter machine guns in the nose and two 12.7 millimeter 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 12.7 millimeter machine guns. The rear fuselage was made deeper to accommodate the turret. There was also a single single flexible 12.7 millimeter 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 1,450 kilograms (3,200 pounds) of bombs, or could be fitted with stub pylons for eight HVARs and an 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.
* One B-25H was fitted with twin Pratt & Whitney 18-cylinder R-2800-51 Double Wasp engines, each offering 2,000 horsepower. The result was designated the "NA-98X Super Strafer". It looked much like a standard B-25H, except that it lacked the blister guns, had big prop spinners unique in the Mitchell line, featured squared-off wingtips, and was given many detail changes.
The Super Strafer first flew at the end of March 1944. The more powerful engines gave it an impressive top speed of 560 KPH (350 MPH), but on 24 April the NA-98X suffered a structural failure during a fast low-level pass and smashed into the ground, killing the two crewmen on board. The USAAF did not proceed further with the variant.
* NAA also proposed a "strafer-bomber" with 18 machine guns, R-2800 engines, and a single tail gun. The USAAF didn't buy the idea, but it did lead to the final Mitchell production variant, the "B-25J". Incidentally, there was no "B-25I", since the USAAF didn't use the "I" code as it was too easily confused with a "1".
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 12.7 millimeter machine guns, and the second was a "strafer" nose with eight 12.7 millimeter 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. Ten of these PBJ-1Js were modified
with underbelly racks to carry a pair of huge 29 centimeter (11.5 inch) "Tiny
Tim" unguided air to ground rockets.
NORTH AMERICAN B-25J MITCHELL:
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spec metric english
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wingspan 20.6 meters 67 feet 7 inches
length 16.1 meters 52 feet 11 inches
height 4.83 meters 15 feet 10 inches
empty weight 8,840 kilograms 19,480 pounds
max loaded weight 19,000 kilograms 41,800 pounds
maximum speed 445 KPH 275 MPH / 240 KT
service ceiling 7,600 meters 25,000 feet
range 2,400 kilometers 1,500 MI / 1,305 NMI
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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.
In 1945, a few B-25Js were fitted to carry "glide torpedoes", which were standard torpedoes fitted with glider wings to give a longer stand-off delivery range. The wings were blown off with explosive bolts before the torpedo hit the water. A few were experimentally dropped against vessels in Japanese waters very shortly before the end of the war.
* Total Mitchell production was as follows:
B-25: 24
B-25A: 40
B-25B: 120
B-25C: 1,620
B-25D: 2,290
B-25G: 400
B-25H: 1,000
B-25J: 4,390
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SUM: 9,884
The exact fate of B-25s intended for the Dutch is extremely complicated and not all that interesting to trace, since under emergency conditions many were diverted to the USAAF. When all the dust had settled, the Dutch had reconstituted flight squadrons under the control of the Royal Australian Air Force.
The Dutch would operate at least 150 Mitchells from Australia through the war. After the war, the Mitchells would see service in the Dutch East Indies in the insurgency that followed, and when the free Republic of Indonesia was established in 1949, they inherited a few of the Dutch Mitchells.
A squadron of Mitchells was also flown by the Dutch from the UK during the war, operating under RAF control and flying both bombing and maritime patrol missions.
After the war, surplus Mitchells were supplied to many Latin American air arms, and the type remained in service there into the 1970s.
* Combat B-25s were often refitted or rebuilt for other purposes, such as reconnaissance, transport, or training, and they would continue to operate in such roles long after the war.
Standard B-25s were often field modified for reconnaissance, but in 1943 45 B-25Ds were converted to a more specialized reconnaissance configuration and designated "F-10". These were stripped of all armament, and fitted with auxiliary fuel tanks in the bombbay and three-direction "trimetrogon" cameras under the nose, giving them odd-looking "cheeks". These aircraft were mostly used for non-combat photographic mapping surveys. Four of them were provided to the RAF late in the war.
A large number of B-25s were formally and informally converted to transports during the war and after. As mentioned, the first B-25 ended up as an NAA company transport, the WHISKEY EXPRESS. Several were converted to posh personal transports, including one for General Dwight Eisenhower and two for General Hap Arnold. NAA converted another B-25 as a company transport after the loss of the WHISKEY EXPRESS, but this aircraft was lost with three crew off the California coast not long after the war.
In 1949, NAA converted a PBJ-1J to an executive transport with a new and distinctive nose in hopes of drumming up business for such conversions. Unfortunately, this aircraft was lost in a crash in 1950, killing seven NAA employees, and nothing more came of the effort.
These conversions were designated "RB-25", where the "R" meant "Restricted" (from combat operations), not "Reconnaissance". A number of late-model B-25s were converted to military VIP transports after 1948 under the designation of VB-25, and some of these remained in military service into the early 1960s.
* The wide availability, good handling characteristics, and flexibility of the Mitchell made it an excellent training platform that gave trainee aircrews the feel of operating a "real" combat aircraft. During after World War II, stripped-down B-25s were assigned to the training role under the somewhat baffling designation of "AT-24".
To confuse matters further, B-25Ds became "AT-24As", B-25Gs became "AT-24Bs", B-25Cs became "AT-24Cs", and B-25Js became "AT-24Ds". In 1948, such Mitchell trainers as survived were given the more rational designations of "TB-25C", "TB-25D", "TB-25G", and "TB-25J", correctly reflecting their original bomber designations.
Many of the TB-25Js were fitted with additional seats and a few other changes in the postwar period, as well as converted into pilot trainers with the designations "TB-25L" and "TB-25N". Most of these modifications were performed by Hayes Aircraft Corporation of Birmingham, Alabama.
Some B-25Js were also modified with special radar installations and operated generally as trainers under the designations "TB-25K" and "TB-25M". These conversions were performed by Hughes. A few B-25Js were used in the Korean war as squadron hacks and electronic warfare platforms.
In civilian hands, Mitchells were used in a variety of roles, including fire-bomber, air freighter, executive transport, test platforms for airborne electronic systems, and even Hollywood flying movie camera platforms.
A large number of B-25s were assembled for a famous hair-raising mass-takeoff scene in Mike Nichol's 1970 movie CATCH-22. A number of Mitchells now survive as collector's warbirds, and a good number of them are still flying, such as BARBIE III, MISS MITCHELL, HEAVENLY BODY, YELLOW ROSE, PANCHITO, and KILLER B. Many of the Mitchells still in the air today were given their refit by Aero Traders of Chino, California.
* The B-25 evolved from the XB-21, and in turn led to a more advanced twin-engine bomber, the "XB-28 Dragon". This aircraft was designed in response to a USAAF requirement for a high-altitude medium bomber, and featured a pressurized fuselage; supercharged R-2800 engines; and remote-control tail, ventral, and dorsal turrets, each with two 12.7 millimeter guns. The turrets were aimed via periscopes. The XB-28 also had three fixed forward-firing 12.7 millimeter guns and a maximum bombload of 1,800 kilograms (4,000 pounds).
While design concepts for the XB-28 started out as modifications of the B-25,
they evolved into a form with more resemblance to a Douglas A-26 Invader,
featuring a single tail and a more streamlined fuselage. Three prototypes
were ordered in 1940, the first flying in April 1942. The second prototype
was cancelled, and the third was completed as the "XB-28A", an unarmed
reconnaissance variant.
NORTH AMERICAN XB-28:
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spec metric english
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wingspan 22.12 meters 72 feet 7 inches
length 17.20 meters 56 feet 5 inches
height 4.83 meters 14 feet
empty weight 11,600 kilograms 25,575 pounds
max loaded weight 16,875 kilograms 41,800 pounds
maximum speed 600 KPH 370 MPH / 325 KT
service ceiling 10,500 meters 34,600 feet
range 3,280 kilometers 2,040 MI / 1,775 NMI
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* I remember being vastly impressed when I was a kid with the massive firepower illustrated by a cutaway of the B-25H that I saw in a book. That big 75 millimeter cannon seemed pretty macho.
Much later, I was disappointed to find out that it wasn't particularly effective. I once read an article written by a B-25 pilot who flew his aircraft in the Agean, nailing German resupply boats. They would sometimes pop off a 75 millimeter round just for fun. One day they actually scored a hit. The pilot and copilot sat there for a moment in amazement, and then one said to the other: "Don't tell anyone we did this, they might think it was a good idea."
* Sources include:
A few items were also taken from a web writeup by aviation enthusiast Joe Baugher.
* Revision history:
v1.0 / 01 oct 99 / gvg
v1.0.1 / 01 apr 02 / gvg / Minor cosmetic update.