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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.
Performance:
Maximum Speed at 13,000 ft: 272mph
Ceiling: 24,200 ft.
Range: 1,350 miles
Armament:
12 12.7-mm (0.5-inch) machine guns
4,000 pounds of bombs
Number Built:
9,889
Number Still Airworthy:
~34
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