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XP-40, P-40A, P-40B,
P-40C
Written by Joe Baugher
The P-40 was the best known
Curtiss-Wright airplane of World War II. It was also one of
the most controversial fighters of the war. It was vilified
by many as being too slow, lacking in maneuverability,
having too low a climbing rate, and being largely
obsolescent by contemporary world standards even before it
was placed in production. The inadequacies of the P-40 were
even the subject of a Congressional investigation. It gets
regularly included on lists of the worst combat aircraft of
World War 2.
All of these criticisms certainly
had some degree of validity, but it is also true that the
P-40 served its country well during the first year of the
war in the Pacific when very little else was available.
Along with the P-39 Airacobra, the P-40 was the only
American fighter available in quantity to confront the
Japanese advance during the first year of the Pacific War.
It helped stem the speed of the Japanese advance until more
modern types could be made available in quantity. The P-40
had no serious vices and was a pleasant aircraft to fly,
and, when flown by an experienced pilot who was fully aware
of its strengths and weaknesses, was able to give a good
account of itself in aerial combat. The P-40 continued in
production long after later types were readily available,
the numbers manufactured reaching the third highest total of
American World War II fighters, after the Republic P-47 and
the North American P-51.
The P-40 was obsolete by European
standards even before the first prototype flew, and it never
did catch up. Its Initial inadequacies in the form of low
firepower and lack of self-sealing fuel tanks or armor were
a reflection of mid-'thirties USAAC requirements which were
outmoded. The P-40 had been developed as basically a
low-altitude close-support fighter under mid-1930s US
tactical concepts which envisaged more need for low-level
ground support operations than for high-altitude
interceptions. The military doctrine of the "ascendancy of
bombardment over pursuit" was dominant in 1937 when the P-40
first appeared. This doctrine assumed that the prospect of
high-altitude enemy air attack on the USA was extremely
remote, with coastal defense and ground attack in the
defense of US territory being seen as the the main tasks for
any future fighter aircraft. Low-altitude performance and
rugged construction received priority over high-altitude
capabilities.
During the war, the Senate Special Committee to Investigate
the National Defense Program (usually known as the "Truman
Committee", after its chairman, Senator Harry Truman of
Missouri) criticized the P-40 on several accounts,
particularly on the original volume purchase of an
inadequate design and its continued production long after
later designs were readily available. However, they finally
concluded that this was not brought about by any undue
favoritism to Curtiss.
Some indication of the enormous
P-40 production program undertaken by Curtiss can be
assessed by its claim on factory floor space and manpower.
During 1941, the Curtiss Airplane Division expanded its
manufacturing area by 400 percent. The total work force was
45,000. This expansion included two new plants, one at
Buffalo, New York and the other at Columbus, Ohio, to
supplement the original Curtiss plant in St.Louis, Missouri.
At the peak of wartime production, the entire Curtiss
Airplane Division complex of factories was producing sixty
aircraft A DAY!
The origin of the P-40 can be traced back to the Curtiss
P-36 (Model 75) fighter, which was powered by a radial,
air-cooled engine. A step in the direction toward what was
eventually to emerge as the P-40 was the XP-37, which was
described in an earlier post. The P-36 design was reworked
to incorporate the Allison V-1710 liquid-cooled V-type
engine, resulting in the XP-37. The XP-37 was equipped with
a General Electrc turbosupercharger, and featured a cockpit
pushed very far to the rear. Thirteen YP-37 service-test
aircraft were built, but problems with the turbosupercharger
caused the development of the P-37 to be abandoned in favor
of a less complex and more straightforward conversion of the
P-36 for the Allison V-1710 engine.
Realizing that the radial-engined P-36A was at the limit of
its development, Curtiss designer Donovan Berlin got USAAC
permission in July 1937 to install a 1150 hp Allison V-1710-19
liquid-cooled engine with integral supercharging in the 10th
P-36A (Serial No 38-10). This project was given the company
designation of Model 75P, and the USAAC gave the project a
new fighter designation, XP-40.
The XP-40 flew for the first time
on October 14, 1938, with Edward Elliot at the controls.
Armament was two 0.50-inch machine guns located in the upper
fuselage deck and synchronized to fire through the propeller
arc, standard armament for US pursuit aircraft at the time.
Wing racks could be fitted for six 20-pound bombs. A small
oil cooler was located beneath the pointed nose. The air
intake for the single-stage supercharger was mounted on top
of the engine cowling between the two machine guns, but
during tests it was replaced by a long cowled intake duct
which became characteristic of all the early P-40 production
models. Initially, the coolant radiator was placed under the
fuselage aft of the wing, but it was gradually moved forward
until it finally ended up located underneath the extreme
nose. The radiator intake was redesigned to include an oil
cooler and two coolers for the ethylene/glycol engine
coolant. The initial XP-40 had a single exhaust port on each
side of the fuselage, but in its final form it had six
separate exhaust ports on each side. The initial XP-40 had
inherited from the P-36 a set of mainwheel fairing plates
which covered the mainwheels when they retracted into their
wing wells, but these were eventually deleted and replaced
by two small doors which closed over the wheel struts upon
retraction.
The maximum speed of the XP-40 was 342 mph at 12,200 feet at
a gross weight of 6260 pounds. This was faster than the
Hawker Hurricane, but slower than the Spitfire or the Bf
109E. Empty weight was 5417 pounds, and fully-loaded weight
was 6870 pounds. Range was 460 miles at 299 mph with 100
gallons of fuel. With 159 gallons of fuel at 200 mph, a
range of 1180 miles was claimed, almost twice that of the
contemporary Hurricane, Spitfire, and Bf 109E. Wingspan was
37 feet 4 inches, wing area was 236 square feet, length was
31 feet 1 inch, and height was 12 feet 4 inches. The
wingspan and wing area were to remain the same throughout
the entire history of the P-40 production run.
In the late 1930s, the USAAC was
planning to expand its force, and on January 25, 1939.
manufacturers were invited to submit proposals for pursuit
aircraft. The Army was still thinking in terms of
low-altitude, short-range fighters. Among the contenders
were the Lockheed XP-38, the Bell XP-39, the Seversky/Republic
XP-41 (AP-2) and XP-43 (AP-4), and no less than three planes
from Curtiss, the H75R, XP-37, and XP-42. Although the XP-40
could not match the performance (especially at altitude) of
the turbosupercharged types, it was less expensive and could
reach quantity production fully a year ahead of the other
machines. In addition, the XP-40 was based on a
already-proven airframe that had been been in production for
some years. Consequently, on April 26, 1939, the Army
adopted a conservative approach and ordered 524 production
versions under the designation P-40 (Curtiss Model 81). At
that time, it was the largest-ever production order for a US
fighter, and dwarfed the service test orders placed that
same day for YP-38 and YP-39 fighters. A couple of weeks
later, 13 YP-43s were also ordered.
The P-40 was similar to the final XP-40 configuration except
for 1040 hp V-1710-33
(C15) engines and provisions for the mounting of one
0.30-inch machine gun in each wing. Flush riveting was used
to reduce drag. Armor, bulletproof windshields, and
leakproof fuel tanks were added in service. The P-40 was a
relatively clean design, and was unusual for the time in
having a fully retractable tailwheel.
The first flight of a P-40 (Ser No 39-156) was on April 4,
1940. Maximum speed was 357 mph at 15,000 feet, service
ceiling was 32,750 feet, and initial climb rate was 3080
feet per minute. An altitude of 15,000 feet could reached in
5.2 minutes. The length of the P-40 was 31 feet 8 3/4
inches, which became standard for all early models. Weights
were 5376 pounds empty, 6787 pounds gross, and 7215 pounds
maximum.
Deliveries of the P-40 to Army units began in June of 1940.
Three of the P-40s were used for service testing, the USAAC
contract making no provisions for the standard practice of
supplying YP models.
Foreign air forces were beginning to take notice of the
P-40, and in May of 1940, the Armee de l'Air of France
placed an order for 140 H-81A (export model of the P-40).
Only 200 of the initial P-40 order
were actually completed as P-40s. Serials were 39-156/280
and 40-292/357. The remaining 324 aircraft of the order had
their delivery deferred to enable Curtiss to expedite the
delivery of the 140 H-81As to France. However, none of these
actually reached France before the Armistice in June 1940,
and the contract was taken over by the Royal Air Force as
Tomahawk I.
16 P-40s were sent to the Soviet Union after the German
invasion. The P-40 lacked such things as armor for the
pilot, self-sealing fuel tanks, and a bulletproof
windshield, so it was not considered as being suitable for
combat. On October 22, 1942, the P-40s still in USAAF
service were ordered restricted from combat duty and were
redesignated RP-40.
The P-40A designation was skipped in the initial designation
assignments. However, it was applied retroactively to P-40
Ser No 40-326 when it was converted to a camera-carrying
photographic reconnaissance model at Bolling Field in March
of 1942.
The P-40B (Model H81B) differed from the P-40 in having an
extra 0.30-inch machine gun in each wing. The engine was
still the V-1710-33.
In September 1940, 131 P-40Bs were procured by the Army to
replace the deferred P-40s. Serials were
41-5205/5304
and
41-13297/13327.
The first P-40B flew on March 13, 1941. The P-40B retained
the same dimensions of the P-40, but weight was increased to
5590 pounds empty, 7326 pounds gross, and 7600 pounds
maximum loaded. Because of the additional weight, the P-40B
had an inferior performance to the P-40, maximum speed being
352 mph, service ceiling being 32,400 feet, and initial
climb rate being 2860 feet per minute. Normal range was 730
miles, but a maximum range of 1230 miles could be attained
at the minimum cruise settings.
The export equivalent of the P-40B
was the Tomahawk IIA (Model H81-A2). They differed from the
American version by having the wing guns replaced by
0.303-inch Brownings. 110 were produced for the RAF. RAF
serials were AH881/990. 23 of these planes were transferred
to the USSR, and one (AH938) went to Canada as an
instructional airframe.
The initial P-40 order was finally completed with 193 P-40Cs
(company designation H81-B). Serials were
41-13328/13520.
The first flight of a P-40C was made on April 10, 1941. The
P-40C retained the 1150 hp Allison V-1710-33
engine, but was fitted with a new fuel system with 134
gallons in new tanks with improved self sealing. In
addition, provisions were made for a 52-gallon drop tank
below the fuselage. The P-40C had a SCR-247N radio instead
of the SCR-283. These additions produced yet another upward
crawl in the weight --- the weights for the P-40C were 5812
pounds empty, 7459 pounds gross, and 8058 pounds maximum
loaded. Consequently, the performance continued to degrade.
Maximum speed was 345 mph at 15,000 feet. Normal and maximum
ranges were 730 and 945 miles respectively. Service ceiling
was 29,500 feet, and initial climb rate was 2650 feet per
minute. Dimensions were wingspan 27 feet 3 1/2 inches,
length 31 feet 8 1/2 inches, height 10 feet 7 inches, wing
area 236 square feet.
The export equivalent of the P-40C was the Tomahawk IIB
(Model H81-A2). A total of 930 were built. RAF serials were
AH991/999 (all to USSR), AK100/570 (36 to China), AM370/519
(64 to China), and AN218/517.
100 of these planes, unofficially designated H81-A3, were
transferred to China where they were used by the American
Volunteer Group --- the famous "Flying Tigers". 23 went to
the USSR, and unspecified numbers went to Turkey and Egypt.
The rest were used extensively by the RAF and South African
Air Force in the North African theatre.
Tomahawk, Flying Tigers, North Africa
Much-rebuilt Tomahawk IIB, recovered from Russia and painted
in the colors of Bob Neale of the AVG. The plane is on
display at the Naval Aviation Museum, Pensacola.
At a very early stage, the Curtiss
P-40 attracted the attention of foreign air forces. On May
10, 1939, the French ordered 140 export versions of the P-40
for the Armee de l'Air. These aircraft were designated Hawk
81-A1 by the manufacturer. The Hawk 81-A1s were identical to
the US P-40 except that they had French instruments and
equipment and were equipped with reverse-movement
"French-fashion" throttles. The first of the French-ordered
H81-A1s flew on June 6, 1940, and a few were actually
completed with French markings. However, before any of their
H81-A1s could be delivered, France surrendered. Britain
agreed to take over the entirety of the French order, and
gave the H81-A the name Tomahawk I in RAF service. RAF
serials were AH741/840 and AH841/880.
The USAAC had agreed to defer deliveries of their P-40s so
that the Tomahawk Is could be supplied to Britain as soon as
possible. The first Tomahawk Is reached England in September
of 1940. The two 0.5-inch machine guns in the nose were
retained, but they were supplemented by four wing-mounted
0.303-inch Browning machine guns in place of the 7.5-mm FN-Brownings
specified by the French. Such was the urgency of their
delivery to Britain that many of the 140 machines still had
French instruments and bore cockpit lettering in French when
they arrived.
However, Britain quickly concluded that these planes were
not suitable for combat, since they lacked armor protection
for the pilot, armor-glass windshields, or self-sealing fuel
tanks. Nevertheless, since a German invasion was feared to
be imminent, they were actually issued to several
operational squadrons.
However, the Hun never invaded England, and so the Tomahawk
Is were used only for training roles within Britain.
Overseas, the first Desert Air Force squadron to be equipped
with Tomahawks was No. 112 which exchanged its Gloster
Gladiators for the Curtiss fighter. No 112 Squadron became
famous for its "shark's tooth" insignia on the engine
cowling, and this scheme was later adopted by the American
Volunteer Group in China. AH774,793, and 840 were sold to
Canada for use as instructional airframes, but they retained
their RAF serials.
The Tomahawk IIA (Model H81-A2)
was equivalent to the US P-40B. It had protective armor and
externally-covered self-sealing tanks. 110 were built for
the RAF under a direct-purchase contract. It carried two
0.30-inch machine guns in the wings in addition to the two
0.50-in guns in the fuselage. A British radio was fitted.
RAF serials were AH881/990. AH938 was transferred to Canada
as an instructional airframe. 23 of these planes were
transferred to the USSR.
The Tomahawk IIB (Model H81-A2) was generally equivalent to
the US P-40C. It had four 0.303-inch Browning machine guns
in the wings in addition to the two nose-mounted 0.50-in
guns. Whereas the Tomahawk IIA had a British radio, the
Tomahawk IIB had US equipment. A total of 930 of these
planes were produced in four lots. RAF serials were
AH991/999, AK100/570 (36 of this batch were shipped to China
and were selected at random with no particular sequence),
AM370/519 (64 were shipped to China, selected at random),
and AN218/517. They were used extensively by the RAF and the
South African Air Force in North Africa starting on June 16,
1941.
After the German invasion of the USSR in June 1941, one
hundred and ninety-five Tomahawk IIBs were shipped to the
USSR, some from the USA, others selected from the reserve
forced based in the United Kingdom in anticipation of the
German invasion which never came. These Russian Tomahawks
went into action on the Moscow and Leningrad fronts in
October 1941, and were the first US-built planes to be used
by the Russians in the new battle area. An unspecified
number of Tomahawk IIBs were sent to bolster Turkish
neutrality in November 1941. Turkey was supplied with planes
from both the Allies and the Axis during World War II.
The Tomahawk IIs were active in
the Middle East from October of 1941 onward. They shared in
the strafing of the retreating Axis troops. The ability of
the Tomahawk to absorb an incredible amount of punishment
became almost legendary. They served with Nos 2, 26, 73,
112, 136, 168, 239, 241, 250, 403, 414, 430 and 616
Squadrons of the RAF. They also served with Nos 2 and 4
Squadrons of the South African Air Force and No 3 Squadron
of the Royal Australian Air Force. At low altitudes, the
Tomahawk II was actually superior to the Bf 109, but this
advantage rapidly disappeared when combat took place at
altitudes above 15,000 feet. The weight which handicapped
the performance of the Tomahawk did have one tangible
benefit --- the rugged structure could absorb a terrific
amount of battle damage and still allow the airplane to
return to base. Although generally outclassed by the Bf 109,
the Tomahawk was a capable fighter in the hands of
experienced pilots such as Neville Duke. Wing Commander
Clive Caldwell of the RAAF scored more than twenty victories
while flying a Tomahawk in the Middle East. However, much of
the opposition to the Tomahawk was provided by obsolescent
fighter biplanes (e.g. Fiat CR-42) and underpowered, lightly
armed fighter monoplanes such as the Fiat G-50 of the Regia
Aeronautica. It had difficulty with the more advanced Macchi
C-202 Folgore.
100 of the RAF Tomahawk IIBs were
released to China and served with the American Volunteer
Group (AVG) --- the famous "Flying Tigers". Company records
list them as Model H81-A3. The Tomahawk IIB was more-or-less
equivalent to the P-40C, but some sources list the Flying
Tiger Tomahawks as being equivalent to the P-40B. There is
confusion on this point.
It is with the Flying Tigers that the P-40 achieved
immortality. Newly-promoted to Brigadier General in the
Chinese Army, Claire Chennault went to the USA in November
1940 to recruit pilots for the AVG. The AVG came into
existence in August 1941. General Chennault ordered 100
P-40s through a loan from the US government. By the time of
Pearl Harbor, some 80 American pilots were serving with the
AVG based at Kunming and Mingaladon. Contrary to popular
understanding, the AVG did not actually enter combat until
AFTER Pearl Harbor. The famous "shark's teeth" marking did
not originate with the Flying Tigers, but was copied from
the markings used by the Tomahawks of the RAF's No. 112
Squadron in North Africa.
The AVG drew first blood on December 20, destroying six out
of ten attacking Japanese bombers. When the AVG encountered
the Japanese Zero for the first time, they initially
underestimated the maneuverability of their opponent, and
they lost two pilots on December 23. [Actually, the Dec. 20
encounter ended with three Kawasaki Ki-48 "Lily" bombers
shot down and one force-landed in Vietnam. The
retractable-gear aircraft that fought the AVG were Nakajima
Ki-43 Hayabusa fighters, later called "Oscar" in the west.]
It was soon learned that it was wise not to mix it up with
the Zero on a one-to-one basis because of the inferior
maneuverability and climb rate of the Curtiss, but instead
to use the P-40's superior speed and diving ability to
advantage. The most effective tactic against the Zero was a
diving pass followed by a rapid departure from the scene.
The P-40 gained a reputation for ruggedness which enabled
many an AVG pilot to return safely home after his plane was
damaged in combat.
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