B 25 Mitchell

North American's response to the US Army Air Corps' Circular Proposal 38-385 for a twin-engined attack bomber was the NA-40, a shoulder-wing design with a tricycle landing gear and capable of carrying a 1,200 lbs (544 kg) bomb load. Armament consisted of 7.62 mm (0.30 in) machine-guns in nose, dorsal and ventral positions. The prototype, built at the Inglewood factory, was first flown by Paul Balfour in January 1939, powered by two 1,100 hp (820 kW) Pratt & Whitney R-1830-S6C3-G engines which were soon replaced by Wright CR-2600-A71 Cyclones each rated at 1,300 hp (969 kW). In this form the aircraft became the NA-40-2 and in March it was delivered to Wright Field for USAAC evaluation, crashing two weeks later as the result of pilot error.

The USAAC was impressed by the promise of the NA-40, however, and North American was asked to continue development of the aircraft for the medium bomber role under the company designation NA-62. September 1939 saw the completion of the basic design of the NA-62 and in that month the type was ordered into immediate production under a USAAC contract for 184 aircraft designated B-25. Several improvements were incorporated, including the widening of the fuselage to allow the pilot and co-pilot/navigator to be seated side-by-side in a cockpit faired into the fuselage, rather than in the tandem glasshouse of the NA-40; the relocation of the wing to a mid-position; and an increase operating weights and bomb load. New engines were also specified, these being 1,700 hp (1268 kW) Wright R-2600-9 Cyclone radials, and a tail gun position was added.

The B-25 was named after the controversial proponent of US air power, William 'Billy' Mitchell, and the first production machine was flown on 19 August 1940. Nine B-25s were completed with the original root-to-tip dihedral before flight tests revealed a degree of directional instability, which was remedied by a reduction in the dihedral angle on the outer wing panels.

The introduction of self-sealing fuel tanks and crew protection armour plating, from aircraft number 25, resulted in redesignation to B-25A. Forty B-25As were built, and this variant was the first to see operational service, with 17th Bombardment Group (Medium) at MeChord Field, scoring the type's first kill on 24 December 1941 when a Japanese submarine was sunk off the US west coast.

Some 120 B-25Bs were manufactured, this model having power-operated dorsal and ventral turrets, each with two 12.7 mm (0.50 in) machine guns. B-25Bs were among the US reinforcements sent to Australia in 1942, serving with the 3rd Bombardment Group's 13th and 19th Squadrons, and were also used for the Tokyo raid, led by Lieutenant Colonel James H. Doolittle, on 18 April 1942. For this attack 16 modified aircraft, with an autopilot, fuel tankage increased by more than 60 per cent to 1,141 US gallons (4319 litres) and the ventral gun turret and Norden bombsight removed, took off from the carrier USS Hornet for an 800 mile (1287 km) flight to their targets at Tokyo, Kobe, Yokohama and Nagoya, flying on to China where most force-landed.

Two USAAF contracts, for 63 and 300 aircraft, were placed for the B-25C which had an autopilot, R-2600-13 engines and additional bomb-racks under the wings and fuselage which could carry, respectively, eight 250 lbs (113 kg) bombs and a 2,000 lbs (907 kg) torpedo for anti-shipping strikes; total offensive load was 5,200 lbs (2359 kg).

Other B-25C contracts included a Dutch order for 162, intended for service in the Netherlands East Indies, although these were never delivered there (and probably diverted to the Royal Air Force), and two Defence Aid-financed contracts, each for 150 and intended for delivery to China and the UK. The basically-similar B-25D was built in a US government- owned but North American-operated factory at Kansas City, where the company manufactured two batches of 1,200 and 1,090 aircraft.

Two machines from the B-25C line were modified for experiments into wing de-icing, these being the XB- 25E with a hot-air system and the XB-25F which used electrically heated elements.

Developed for attacks on Japanese shipping, the B-25G carried a 75 mm M4 US Army cannon mounted in the nose, the cannon being provided with twenty-one 15 lbs (6.8 kg) shells. The armament was supplemented by a pair of 12.7 mm (0.50 in) guns which were used also to aim the heavier weapon. in addition, the dorsal and fully- retractable ventral turrets each contained two machine guns. Five B-25Cs were, in fact, completed as B-25Gs, and 400 were subsequently built at Inglewood. This version was initially assigned to the US Far East Air Forces, entering service with the 498th Squadron in February 1944.

The Mitchell with the greatest firepower was the B-25H, of which 1,000 were built at Inglewood. The 75 mm cannon was of the lighter T13E1 model and the four 12.7 mm (0.50 in) guns, also mounted in the nose, were augmented by two similar guns in blisters on each side of the fuselage below the cockpit. The twin-gun dorsal turret was relocated to a position just aft of the cockpit, and armament was completed by a 12.7 mm (0.50 in) gun in each of the waist positions and two in the tail. Additionally, the B-25H could carry a 3,000 lbs (1361-kg) bomb load and a torpedo, as could the B-25J in which the glazed nose with its bomb aiming station was reintroduced, reducing the nose armament to one hand-operated and four fixed 12.7 mm (0.50 in) guns. Some later aircraft had a solid nose with eight 0.50-in (12.7-mm) guns, bringing the total of these weapons to 18. Underwing racks could carry eight 5 in (127 mm) rockets. The USAAF contract was for 4,805 B-25Js, but as the war ended 415 were cancelled and 72 were completed but not delivered; all were manufactured at Kansas City.

For reconnaissance duties the F-10 version was introduced in 1943, 10 being converted from B-25Ds. Armament was removed, additional fuel tanks fitted in the bomb bay, and cameras installed in the rear fuselage and in the nose.

Sixty B-25Ds, B-25Gs, B-25Cs and B-25Js were converted during 1943-4 for use as advanced trainers under the designations AT-25A, AT-25B, AT-25C and AT-25D. They were later redesignated TB-25D, TB-25G, TB-25C and TB-25J; more than 600 of the last model were converted after the war and between 1951 and 1954 117 and 40 Mitchells were respectively converted to TB-25K and TB-25M standard, as flying classrooms for instruction in the use of Hughes E-1 and E-5 fire-control radar. The final training versions were the TB-25L and TB-25N multi-engine conversion trainers, of which Hayes Aircraft Corporation produced 90 and 47 examples respectively.

US Navy Mitchells, of which delivery began in January 1943 with an initial assignment to VMB-413, comprised 50 PBJ-ICs, 152 PBJ-IDs, one PBJ-IG, 248 PBJ-IHs and 255 PBJ-IJs, the letter suffix identifying the equivalent B-25 variant.

The advent of the Mitchell allowed the Royal Air Force to replace the Douglas Bostons and Lockheed Venturas flown by No. 2 Group on daylight operations. The first 23 aircraft, delivered in May and June 1942, were B-25B Mitchell Is, three of which were subjected to evaluation and acceptance trials at the Aircraft and Armament Experimental Establishment; of this batch one was retained in Canada and another crashed before delivery. The rest were flown to Nassau in the Bahamas where No. 111 Operational Training Unit had been established on 20 August, based at Windsor and Oakes Fields. Between May 1943 and June 1945, No. 13 OTU also flew Mitchells from Bicester, Finmere and Harwell in Britain.

As deliveries of B-25C Mitchell lis built up through the second hall of 1942, Bahamas-trained crews returned to the United Kingdom to form the first squadrons, originally to have been Nos. 21 and 114. In fact, the first two operational units were Nos. 98 and 180 Squadrons, formed at West Raynharn on 12 and 13 September, respectively. The Dutch-manned No. 320 Squadron gave up its Lockheed Hudsons for Mitchells at Methwold in March 1943, and No. 226 replaced its Bostons at Swanton Morley in May. All four squadrons flew Mitchells until after the cessation of hostilities.

After initial problems with the Mitchell's armament had been solved, RAF operations began on 22 January 1943 when six aircraft from No. 98 Squadron and six from No. 180 attacked oil installations at Ghent. The four squadrons of No. 2 Group continued their formation attacks throughout 1943 and 1944, operating increasingly in a tactical role following the Allied invasion of France in June 1944. Nos. 98, 180 and 320 Squadrons moved up to Melsbroek, Brussels in October, while No. 226 took up residence at Vitry-en-Artois. The last No. 2 Group Mitchell operation of the war was flown on 2 May 1945 when 47 aircraft attacked marshalling yards at Itzehoe. RAF Mitchell operations outside of Europe included those of Nos. 681 and 684 Squadrons, flying in a photographic reconnaissance role in India from 1943 to 1945.

A North American B-25H of 1st Air Command Group 10th Air Force USAAF - Hailakandi, India 1944

RAF serial batches covered 886 Mitchells, comprising 23 B-25B Mitchell Is; 432 B-25Cs and 113 B-25Ds, both of which were known as Mitchell lls; and 316 B-25J Mitchell Ills. The remaining two were B-25Gs, with the 75 mm gun, and one of them, with armament removed, was probably the last in service in the United Kingdom, flying with the Meteorological Research Flight at Farnborough as late as 1950.

In addition to the Dutch-manned No. 320 Squadron, RAF Mitchell units manned by foreign nationals included No. 305, whose Polish crews converted from Vickers Wellingtons at Swanton Morley in September 1943, and No. 342 (Lorraine) Squadron which exchanged its Bostons for Mitchells at Vitry-en-Artois in March 1945. After disbandment as RAF units both the French and Dutch took their aircraft home.

No. 320 Squadron was reformed at Valkenburg as a Dutch navy patrol/search and rescue unit on 29 March 1949, its initial equipment including Mitchells which, replaced by Lockheed Harpoons when the squadron changed role to maritime patrol, were passed on first to No. 5 Squadron, formed on 7 May 1951, and then to No. 8 Squadron on 10 March 1952.

During the war the Dutch had flown Mitchells at the Royal Netherlands Military Flying School at Jackson, Missouri and with No. 18 (Netherlands East Indies) Squadron of the Royal Australian Air Force, formed with Dutch personnel at Canberra on 4 April 1942, and operating throughout the campaigns to recapture the Pacific islands. Control passed to the Netherlands on 15 January 1946 and, based at Bandoeng in Java, the squadron was soon in action again, in the conflict with the Indonesians. After the ceasefire, which resulted in the disbandment of the Netherlands East Indies air force on 21 June 1950, Mitchells were handed over to the new Indonesian government to form the equipment of the bomber flight of No. 1 Squadron. The RAAF acquired 50 Mitchells, including B-25Ds and B-25Js, which were flown by Nos. 2 and 119 Squadrons.

The Mitchells supplied to the Chinese air force remained in service throughout the postwar struggle which led to the communist overthrow of the Chiang Kai-shek government, some captured aircraft being used by the Sino-Communist forces while others escaped to Taiwan. A total of 807 Mitchells was supplied under Lend-Lease to the USSR, although eight were lost in transit.

In Central and South America, Mitchells were supplied to Brazil, Chile, Mexico and Uruguay. Signature of the Rio Pact of Mutual Defense in 1947 resulted in the United States supplying B-25Js to Brazil, Colombia, Cuba, Peru and Venezuela.

Among Commonwealth air forces, the Royal Canadian Air Force received a small number of Mitchell lls from the Royal Air Force in May 1944 and these, modified to the standard of the USAAF F-10 version with cameras installed in the nose, equipped the Photographic Flight at Rockcliffe, Ottawa. The unit was unofficially designated No. 13 (Photographic) Squadron, as part of No. 7 (Photographic) Wing, although this title was not formally promulgated until 15 November 1946. The squadron was renumbered as No. 413 (Photographic) Squadron on 1 April 1947 and the Mitchells served alongside Avro Lancaster Xs until withdrawn in October 1948.

Auxiliary squadrons formed after the war includes Nos. 406 and 418 Squadrons, based at Saskatoon and Edmonton respectively. Both were light bomber units, flying Mk 11 and Mk 111 Mitchells until they were retired in 1958. VIP-configured Mitchells were used by No. 412 Squadron between 1956 and 1960. 

Nicknames: Billy's Bomber (after General Billy Mitchell); Bank (NATO code name for Russian Lend-Lease B-25s).

Specifications (B-25J):

Engines: Two 1,700-hp Wright R-2600-92 Cyclone radial piston engines
Weight: Empty 19,480 lbs., Max Takeoff 35,000 lbs.
Wing Span: 67ft. 7in.
Length: 52ft. 11in.
Height: 16ft. 4in.

Maximum Speed at 13,000 ft: 272mph
Ceiling: 24,200 ft.
Range: 1,350 miles

12 12.7-mm (0.5-inch) machine guns
4,000 pounds of bombs

Number Built: 9,889

Number Still Airworthy: ~34