Navy Lieutenant Edgar G. Osborne looked at his watch. It was 8:20 in the morning of April 18, 1942. The flight deck officer flagged Lt. Col. Doolittle in the lead aircraft to take off into the 40 knots headwind. One after one the 16 aircraft accelerated down the deck of the carrier, reaching takeoff speed in just 450 feet. Dipping slightly off the end of the bobbing runway, they wobbled skywards for their nearly 700 mile voyage to the Japanese empire. The Doolittle Raid was underway.

Background

The North American Aviation B-25 Mitchell was reputedly the best medium bomber of World War II. It was built in larger numbers than any other US twin-engine bomber, it served on all fronts and was supplied to the Soviet Union, Holland, Australia, Brazil and the UK.

In 1937, US Army Materiel Division wanted a twin-engine bomber with longer range and the ability to carry higher payloads than the existing single-engine types in service. They wanted it to fly 1200 miles at 200 mph/174 kts, carrying 1200 pounds of bombs. The circular proposal was sent out in March 1938.

Proposals were submitted by Boeing-Stearman, Bell, Douglas, Martin and North American Aviation. North American's design NA-40 was selected, and in January 1939 it flew for the first time. Except for the unimpressive XB-21 Dragon, North American Aviation had previous experience with neither twin-engine designs nor bombers.

The crew of five was considered large for an aircraft in the attack role. The two pilots were seated in tandem up front, the radio operator and gunner were in the aft fuselage and the bombardier/navigator's office was in the all-glass nose.

Armament consisted of three 0.30in/7.62mm machine guns; one in the nose, one in a dorsal turret behind the cockpit and one which could be moved between different cut-outs in the aft fuselage. Compared to the ultimate version of the B-25, this armament was akin to shooting rubber bands.

The engines were a pair of Pratt & Whitney R-1830s rated at 1100hp each, driving two twelve foot three blade propellers.

On January 29, 1939, the NA-40 flew for the first time. Behind the controls was North American test pilot Paul Balfour. Among the many things uncovered during the first test flights was the fact that the NA-40 was seriously underpowered. In february 1939 the Pratt & Whitney engines were replaced by Wright R-2600 Double Cyclones. Each of these fourteen cylinder air-cooled radial monsters yielded 1600hp, enough to propel the aircraft to 286 mph/249 knots at 5000 ft. After the engine switch, the designation changed to NA-40B. On April 11, 1939, the NA-40B crashed during an engine-out test. Although the crew escaped injury, the aircraft was completely destroyed by fire.

Even though the accident was found not to be caused by the aircraft, the US Army Air Corps (USAAC) decided not to proceed with the North American design. The order went to Douglas Aircraft Company and their DB-7 model instead. It became the Douglas A-20 Havoc in USAAF service.

North American's next attempt

In March 1939 the Army Air Corps issued a new proposal for the design of a medium bomber. North American took the NA-40B design, improved it and submitted it as NA-62. The new design was slightly larger, could carry more payload and had greater range. The tandem cockpit of the NA-40B was replaced by a side-by-side cockpit, thus changing the entire nose layout of the aircraft. The NA-62 retained its crew of five and got an extra 0.50in/12.7mm machine gun in the tail.

On August 10, 1939, the US Army Air Corps ordered 184 NA-62s directly off the drawing board. Its official designation became B-25 Mitchell. The idea for the name came from Lee Atwood, North American's vice president and chief engineer

The B-25 was named after Colonel William C. "Billy" Mitchell who was an outspoken advocate for air power. In the 1920's, the take on aircraft was that they were best suited for observation. Colonel Mitchell opposed this view, arguing for air power in its own right. He was court-martialed for insubordination because of this. He was however ultimately proven right, and posthumously promoted to Brigadier General.

The B-25 was accepted by the US Army in February 1941. One of the first B-25s ever built was modified into General Henry H. "Hap" Arnold's personal transport. This particular aircraft is still airworthy today, carrying the US civil registration number N2825B. It was also owned by Howard Hughes at one time.

The very first B-25 built was retained by North American as a company transport. It had seats, windows and other civilian conveniences fitted. It was named Whiskey Express and served NAA until an unfortunate belly landing in 1945 which saw it off to the scrap heap.

Variant B-25A

In February 1941, the B-25A emerged from the factory with crew armour and self-sealing fuel tanks. The engines didn't change though, resulting in a slight speed and range penalty on the Mitchell. Some of the 40 B-25As built were assigned to coastal defence, one claiming the sinking of a Japanese submarine off California on December 24, 1941.

Variant B-25B

The defensive armament of the Mitchell was found to be less than effective. 0.30in/7.62mm aircraft guns just doesn't pack enough punch unless they have a ridicolously high rate of fire (as evidenced by the 1960s' multi-barreled miniguns), so the waist and tailguns were replaced with two dual 0.50in/12.7mm turrets. One turret was on the top of the rear fuselage and manned. The other was a retractable belly turret operated and sighted remotely from the cockpit. The belly turret was usually removed in the field because of its poor design. To fire the remote controlled guns, the gunner had to kneel down and look through a periscope system while handling the dual firing controls, becoming dizzy and nauseous in the process. It took almost a full minute to lower the turret, and sometimes it wouldn't even come back up again.

A man could learn to play the fiddle good enough for Carnegie Hall before he could learn to fire that thing.
- Colonel Doolittle describing the ventral gun turret

The final B-25B was delivered in January 1942, completing the original USAAF contract for 184.

NAA delivered 23 B-25Bs to the British RAF as "Micthell Mark I" as well as a small number to the Soviets. 40 B-25Bs originally destined for the Dutch Air Force were diverted for USAAF use.

The sixteen Mitchells that took off from USS Hornet for what became known as The Doolittle Raid were B-25Bs.

Variants B-25C and B-25D

The C- and D-variant of the Mitchell was more or less identical. The reason for this variant numbering is simple: the USAF was desperate for the Mitchell and wanted as many as they could get and as soon as possible. To meet these demands NAA erected a new factory in Kansas City, Missouri to build the 2290 ordered B-25Ds. The 1625 B-25Cs would be built at NAA's Inglewood, California plant.

After adding more firepower, more fuel, longer wings and generally letting the Mitchell's weight creep upwards in the A and B variant, NAA decided to finally replace the old engines with a pair of Pratt & Whitney R-2600-13 Double Cyclone engines. The new powerplants had a 1700 horsepower rating, giving the aircraft a maximum speed of 284 mph/247 knots at takeoff.

The Royal Air Force received 367 B-25Cs and 212 B-25Ds which they used extensively as "Mitchell Mark II". In RAF service the Mitchell Mk. II got its baptism of fire on January 22, 1943. On that day, six aircraft from 98 and 180 Squadron attacked oil installations in Ghent, Belgium. The attack didn't work out very well since RAF found itself lacking a bit with regard to tactics. Pounded by ground fire and enemy fighters, only three of the six aircraft returned.

As the production of Mitchells continued, a lot of changes were made to armament and design. The 0.30in/7.62mm single nose gun was replaced with a single 0.50in/12.7mm gun. In addition, a single 0.50in/12.7mm gun was added to the starboard side of the nose. Some B-25C variants got underwing bomb racks so that the maximum bombload could be increased from 3000 to 5200 pounds.

The amount of fuel it could carry also increased to 974 U.S. gal./3687 litres. This gave the Mitchell a range of 1500 miles/2414 km with 3000 pounds of bombs. To give the crew a little convenience on long trips at high altitudes, a cabin heater was also put in.

In addition, a lot of other minor changes and combat modifications were done both in the field and in NAA's factories as combat reports came back.

The US Marine Corps also used variants of the Mitchell called PBJ-1C and PBJ-1D. These were significantly modified B-25C and B-25D Mitchells. Most importantly, they sometimes had a search radar in the nose and the ability to carry mines, depth charges and torpedoes. Later USMC Mitchells had provisions for ten HVAR (High Velocity Air Rocket) rockets.

General Kenney and Colonel "Pappy" Gunn

Two USAAF officers influential on the Mitchell's further developments were Major General George C. Kenney and Colonel Paul I. "Pappy" Gunn. Kenney was in charge of the pacific 5th Air Force under General Douglas MacArthur. Together with Colonel Gunn he devised several Mitchell modification schemes which gave the aircraft terrifying firepower in ground attacks.

The lone 50 caliber in the nose was substituted by Colonel Gunn and NAA for a devastating set-up; four caliber 50 guns sticking out of the nose and two or four more in "blister packs" under the cockpit. Eight 0.50in/12.7mm guns firing simultaneously at a target pretty much guarantees something will happen to it.

Together with the added firepower also came the tactics of anti-shipping skip bombing. General Kenney was not your ordinary desk type commander and had some fairly original ideas on how the enemy should be thrown out of the South Pacific. Pre-war doctrine on shipping strikes dictated bombing from medium or high altitude. That is at least 10.000ft/3300m up in the air. Kenney and Gunn found that from such heights hitting anything with free-falling bombs was anything but easy, especially when faced with intense anti-aircraft fire.

What they came up with instead was skip bombing. Coming in at very low level riddling the enemy ship with all eight forward machine guns, a time-delayed bomb was dropped at a preset distance from the target. The bomb would skip across the sea and explode in the ship after the Mitchell had pulled up and flown away.

Albeit very dangerous, this proved to be a devastatingly effective attack.

Variant B-25G

NAA considered a few increases in firepower themselves, the biggest and most fearsome-looking was the M-4 75mm nose cannon. The M-4 was a standard Army issue 75mm originally developed in France during World War I. Inside the extensively modified aircraft nose, a moving cradle and a spring mechanism was fitted to absorb the recoil. An armoured rack with 21 shells for the cannon was also fitted.

The only aircraft to have a bigger gun than the B-25G Mitchell was the contemporary experimental Italian Piaggio P.108A and the post-war Lockheed AC-130 Spectre gunship, both with 105mm guns.

The rest of the G-variant armament was generally similar to the C/D variant; gun turrets on top and bottom and no guns in the tail. In the middle of the B-25G production run, the bottom turret was deleted and never appeared on the Mitchell again.

The impressive appearance of the G-variant only looked good on paper though. In the field the manually loaded 75mm cannon was found to be lacking with regard to aiming and rate of fire. A pair of 0.50in/12.7mm guns in the nose were supposed to help the pilot in aiming and ranging the 75mm gun. Because of the differences in trajectory from the big shells, the guns proved useless for both aiming and ranging. As a result of this and the ever dwindling number of targets for the big gun, it was rarely used.

Variant B-25H

By now the B-25 had firmly entrenched itself as the low level attack aircraft of choice from the South Pacific to the Mediterranean theater. The H variant was largely similar to the G except for the usual nose armament experiments. A lighter 75mm gun was fitted to the nose and the two 0.50in/12.7mm machine guns got the company of two more. An additional two machine guns were mounted on the fuselage starboard (later two more on the port) side. The top turret was moved forward to counter the bigger and more comfortable tail turret. Both turrets had dual machine guns.

The Mitchell were now armed with fourteen 0.50in/12.7mm machine guns, one 75mm cannon, HVAR rockets, 3200 pounds of bombs or a torpedo and 5600 rounds of caliber 50. An impressive array of firepower indeed.

A controversial change on the H variant was the removal of the co-pilot. Leading figures in the USAAF disagreed on the necessity of a co-pilot, but in the end the USAAF boss General "Hap" Arnold eventually settled the argument and ordered the H variant delivered without provisions for a second pilot.

The five man crew now consisted of pilot, navigator/radio operator/cannoneer, flight engineer/dorsal gunner, waist gunner/camera operator, and tail gunner.

The final B-25H was delivered in July 1944.

Variant B-25J

The J variant was the final and most numerous Mitchell produced. It was exclusively built at the NAA Kansas City plant, the Inglewood factory having switched to production of the P-51 Mustang.

The main task of the Mitchell was once again bombing from medium height, although a solid eight-gun nose could be fitted which gave the aircraft a total of eighteen 0.50in/12.7mm machine guns.

A lot of small changes and provisions for different types of bombs were made to the J variant, but the most important change was putting the co-pilot back in, bringing the crew up to six.

The B-25 and the Empire State Building

On July 28, 1945 a USAAF B-25 Mitchell hit the 78th and 79th floor on the north side of the Empire State Building while flying through thick fog. Its destination was Newark, New Jersey. Fourteen people died from the crash and dozens were injured. Witnesses saw a plane sticking out of the skyscraper fearing the worst. USA were still at war, and many people believed New York City had come under attack.

The building withstood the impact of the 10 tonnes of aircraft flying into its structure, although it took three months to repair the $1.000.000 worth of damage.

The post-war B-25

In August 1945, the day after the war in the Pacific ended, NAA's Kansas City plant was closed down. The Mitchell outnumbered all other medium bombers in USAF service and was soon converted into advanced pilot trainers. It soldiered on in this role until January 1959. A lot of Mitchells were sent to the US Air National Guard as support for F-89 Scorpion and F-94 Starfire fighter intercept squadrons. Others were utilized as weather reconnaissance and personnel transports. A few Mitchells were used in the Korean War as electronic warfare aircraft.

Being the most prolific surviving warbird, the Mitchell have also seen extensive civilian use. A large number of surplus Mitchells were bought as executive transports, of course with both the exterior and interior getting a thorough redecoration.

Another use for the Mitchell was in the field of civilian firefighting. The US Forest Service bought a considerable number of surplus Mitchells, installed huge water tanks in the main fuselage and sent them out to waterbomb forest fires. Firefighter Mitchells can be seen in the 1992 Mel Gibson/Jamie Lee Curtis movie Forever Young.

In the movie Catch-22, a big number of Mitchells can be seen in various flying scenes. The movie and book main character Yossarian is a pilot on a B-25.

Finally, early Cinerama film work used a converted B-25 as a camera platform for Hollywood aerial shoots.

Out of the about 150 surviving Mitchells, around 40 are still airworthy today. Among them are Barbie III, Yellow Rose, Heavenly Body, Miss Mitchell, Panchito and Killer B. The next time you are at an air show, look out for one of these warbirds usually refitted by Chino, California company Aero Traders.

The B-25 in other Air Forces

The B-25 Mitchell flew with many different Air Forces during and after World War II:

  • Dutch Air Force until 1951
  • Royal Australian Air Force. Until 1945.
  • Royal Canadian Air Force. Mostly post-war use until 1960.
  • Soviet Air Force. 870 delivered. Got the NATO reporting name Bank after the war.
  • Nationalist China air force in China, later Taiwan. Over 100 delivered.
  • French Air Force. 21 delivered. Scrapped in 1947.
  • Brazil. 92 delivered. Used until 1970.
  • Royal Air Force, UK. 910 delivered.
  • Bolivia. 13 delivered. Used at least until 1979.
  • Chile. Twelve delivered. Replaced in 1954.
  • Colombia. Three delivered. Used until 1957.
  • Cuba. Four delivered. Used until 1959 at least.
  • Mexico. Three delivered. Used until the 1960's.
  • Peru. 20 delivered in 1947. Used until the 1960's.
  • Uruguay. 14 delivered.
  • Venezuela. 39 delivered. Replaced in 1971.

Production numbers

A total of 9884 B-25 Mitchells were built by North American Aviation. This is a breakdown of numbers by variant:

	B-25:	  24
	B-25A:	  40
	B-25B:	 120
	B-25C:	1620
	B-25D:	2290
	B-25G:	 400
	B-25H:	1000
	B-25J:	4390

Sources:
  • "North American B-25 Variant Briefing" by Robert F. Dorr, Wings of Fame, Volume 3, 1996
  • Joe Baugher's excellent site at http://www.csd.uwo.ca/~pettypi/elevon/baugher_us
  • ABC News' news archives at http://www.abcnews.com
  • "The B-25 Mitchell", Greg Goebel <http://www.vectorsite.net/avb25.html>

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