In 1935 Curtiss-Wright built one of the first of a new breed of sleek, all-metal American fighter
aircraft. Though it had a pretty disastrous beginning, and an uneventful service life with
US pilots, it would go on to serve extensively overseas with a variety of countries in the lead
up to and during the Second World War. We are of course talking about the Curtiss P-36 Hawk.
In the early 1930s the Army Air Corps had been forced to accept that the era of the biplane
was drawing to a close. Despite being hobbled by the financial effects of the Great Depression,
development had progressed on a new generation of bomber aircraft, the best examples being the
Boeing B-9, and the Martin B-10. This put the Army in the rather
embarrassing position of having bombers that were faster than their best pursuit aircraft.
And while the Boeing P-26 sort of corrected this, its design was already considered outdated after
a couple of years of service. And so, in the spring of 1935, the Army opened a competition
for the development of a modern pursuit fighter. The aircraft design submitted by Curtiss
was the model 75. This was a departure from previous models as the principal designer was
Donovan Berlin, who had previously worked for Northrop. The model 75 was a low-wing monoplane
of all-metal construction – with the exception of the control surfaces which were fabric.
It was to have a fully enclosed cockpit with a sliding canopy, a fully retractable undercarriage
with the main wheels slotting into the wings, and Construction of the prototype began in 1934.
At this time, it was a completely private venture by Curtiss, though they were expecting the Army
Air Corps to announce a design competition at some point in the near future. As it turned out, their
metaphorical crystal ball was almost accurate to the day and the prototype took off in May 1935,
the same month as the announcement of the. The prototype performed well during the
initial tests, with the sole exception that its maximum speed was slower than expected.
Its engine was an experimental two-row 14 cylinder version of the Wright Whirlwind,
dubbed the XR-1670-6, and it would become a source of frequent mechanical headaches.
Nevertheless, Curtiss were generally satisfied with their prototype,
as was the Army, and it was sent to Wright field to take part in the competitive trials.
These trials took some time to get underway, owing to the lack of competing aircraft, and it turned
out that the prototype submitted by Curtiss was the only one to actually arrive on time.
The prototype developed by Seversky – considered the main rival for Curtiss – had been heavily
damaged during a delivery incident and had to be returned for repairs…during which
it was changed from a two-seater, fixed-gear fighter into a more competitive single-seat
model with a retractable undercarriage. This would become the basis of the Seversky P-35.
The only other major competitor was the almost completely unknown Northrop 2a, which remained
unknown as during its maiden flight on July 30th it took off, headed out over the Pacific Ocean,
and promptly disappeared. The pursuit fighter competition
was delayed to allow Seversky to rebuild their prototype, this prompted Curtiss to protest,
claiming that Seversky were now being given an unfair advantage as they were actively modifying
their prototype, rather than just repairing it. As a result the competition was then
further delayed until 1936 so that Curtis could then make their own modifications.
The experimental Wright engine was replaced with a 700hp Pratt & Whitney R-1535. However,
concerns were soon raised about a potential lack of power, and the engine was changed again
to a 950hp 9-cylinder Wright Cyclone. During this delay, the opportunity was also taken to
strengthen the canopy and adjust the fuselage behind the cockpit to improve rear visibility.
Unfortunately, the new engine proved to be as cantankerous as the old one. No less than four
engine changes were made during the trials at Wright field, and the aircraft’s top speed was
still slower than expected. As a result of this the Seversky prototype would win the competition,
earning a contract ordering 77 models under the new designation P-35.
For Curtiss the disappointment was short lived. The Army Air core had reservations about
Seversky’s capacity to meet delivery requirements, and combined with the growing sabre rattling in
Europe, they decided a backup aircraft was needed. And so, on the 16th of June 1936 Curtiss received
an order for three service test models of the 75B that were redesignated as the Y1P-36.
The first of these was delivered to the Army in March of 1937. The main differences between the
prototype and the test model were the change to the 900hp Pratt & Whitney twin wasp engine,
and further modifications to the rear cockpit to again further improve rear visibility. The
Y1P-36 was a significant improvement over the original prototype, and it so thoroughly
impressed the Army that it won a new pursuit fighter competition in 1937 and orders were
placed for 210 production aircraft as the P-36A. This was the largest single order for military
aircraft in the US since the first world war, but it would not be the only order
Curtiss would receive. Indeed, most of the P-36 fighters produced would be the various
export models – however I’ll cover the domestic versions first to keep things simple.
The first production model, the P-36A, arrived at Wright field in April of 1938. The 20th Pursuit
group, based at Barksdale Field in Louisiana, had been the intended first recipient of the
new fighter, and expecting this they had chosen to relinquish their old P-26s ahead of time.
Unfortunately, upon arriving, the P-36s almost immediately encountered an extensive array of
teething problems. Severe buckling of the metal skin was observed near the landing gear wells,
which required adding reinforcements and thickening the skin.
Engine exhaust difficulties threatened to either A) rob the aircraft of power,
or B) threaten self-immolation, and despite fixes on the production line and in the field,
numerous P-36s were repeatedly grounded. This was the cause for some embarrassment
for both Curtiss and the 20th Pursuit group, as at one point they were left with just six operational
fighters between three squadrons, with many pilots lamenting the loss of their old peashooters.
Some of these problems took a considerable amount of time to fix,
and by that time the P-36A was being relegated to the training role in the US. Development was
considerably underway on the newer, more powerful P-40 (which had taken the painful lessons of the
P-36 to heart) and the only combat experienced by US P-36s was during the attack on Pearl Harbour,
during which five were able to get into the air and shoot down a pair of Japanese Zeros.
Attempts had been made to improve the P-36 in the US,
but they didn’t have much of an impact overall. A single P-36B was produced in 1938.
It was fitted with a 1100hp supercharged twin wasp to evaluate the engines supercharge gearing,
but it was eventually converted back to a P-36A at the conclusion of the tests.
The last 30 models of the original order for 210 aircraft were converted to the P-36C. These had
a 1200hp Twin-Wasp engine and an additional pair of 30 calibre machine guns mounted in the wings.
Experiments were also made with a complete change of the powerplant. The XP-37 and the
thirteen subsequent test models were powered by the Allison V-1710 liquid-cooled engine.
The experimental prototype first flew in June 1937 and the army was impressed by its performance.
Unfortunately, it was a short-lived project, problems around the supercharger led to
multiple delays, and the high cost of each completed aircraft sealed its fate.
So yes, overall, the P-36 didn’t have a very exciting life with the US armed forces, but it did
significantly better overseas. A large number were exported to various countries around the world,
and during World War 2 many captured aircraft were brought into service with other powers.
This led to one of the few occasions during the conflict in which American-built planes
fought against other American-built planes. Early in 1937, Curtiss began development work
on a simplified version of the Y1P-36 to be sold for export. Not all overseas
customers enjoyed climates or budgets that were kind towards complicated aircraft,
and sophisticated features like a retractable landing gear threatened all kinds of maintenance
problems, and so the model 75H was developed. In general, its construction was similar to that
of the Y1P-36, but it had a fixed landing gear and a lower powered engine of 875hp.
Emphasis was placed on ease of maintenance, rough field performance,
and the aircraft’s capacity to accommodate different types of engines and armament.
The first overseas customer for this aircraft was China, who placed an initial order for 112
units at the end of 1937. These aircraft were retroactively designated as the Hawk
75M by Curtiss. It is unclear how many of these actually ended up in Chinese service as Only 30
Hawk 75Ms are accounted for in Curtiss records, with deliveries beginning in May of 1938. Tooling
equipment and kits for an unspecified number of additional aircraft were also delivered, but there
seem to be no records of any more aircraft being assembled. In total, three full squadrons of Hawks
are known to have been operated, but they achieved little success against the Japanese forces,
largely due to poor serviceability and the inadequate training of pilots and ground crews.
The simplified version of the Hawk was also exported to a few other countries under
different designations: Thailand operated the Hawk 75N, and Argentina operated the Hawk 75O.
Argentina also acquired a license to manufacture the 75O domestically, with 20 units being built
at a supposedly better standard than the export models that were delivered to them.
Along with the simplified Hawk, Curtiss also exported production versions of the P-36A,
with most of them going to European nations.
The French Air Force would be the largest foreign operator of the P-36,
and it was one of their most fielded aircraft at the time of the German invasion in 1940.
French interest in the P-36 dated back to 1938, when the government entered into negotiations with
Curtiss to supply them with 300 export models. The Hawk 75A was an export model of the P-36A and
could be sold with either the Pratt & Whitney Twin Wasp or the Wright Cyclone engine. Unfortunately,
these negotiations were fraught with difficulty; the unit price asked by Curtiss was high enough
to be considered insulting, and the Army Air Corps opposed the deal as they doubted
Curtis could meet both their own delivery requirements and those of the French.
However, with Hitler eyeing off bits of Europe with the hunger of a bear in spring,
the French need for military equipment was growing by the day.
This was further compounded by development issues encountered in France with their own aircraft,
and so in mid-1938 an initial contract was signed for 100 units of the Hawk 75A-1. This was partly
made possible due to the personal intervention of President Roosevelt, who allowed the French
test pilot a chance to fly the Y1P-36 and report his findings back to the French government.
Between 1938 and the Armistice between France and Germany, multiple orders were placed for the Hawk,
and the design of the export model would be changed several times. In France the name of
Hawk was never used, and the aircraft were known simply as the H75. Not counting for units lost in
delivery and those never assembled for combat, the strength of French Hawks totalled 291 aircraft.
They saw action within the first month of war in Europe, with units from the Groupe de Chasse
2/4 shooting down a pair of Messerschmitt Bf 109Es in September 1939 – claiming the
first allied arial victories of the conflict. Generally, they were outclassed by the Bf109,
being neither as fast or as well armed, but their superior manoeuvrability and ability
to take more punishment helped to even things out. During the fighting through 1939 and 1940,
French pilots claimed 230 air-to-air kills and 81 probable against a loss of just 29
H75s. Though potentially optimistic, it would mean that just over one third of all French
kills during the battle of France were made by an aircraft that made up less than one
sixth of its single-seat fighter force. After the collapse of French resistance,
the aircraft that had not escaped across the Channel were captured by the Luftwaffe,
in fact some of them had not even been assembled and were still in their delivery crates.
These aircraft were taken back to Germany where they were overhauled and re-fitted with German
instrumentation before being sent to Finland. In total, the Finnish Air Force would receive 44
captured aircraft between 1941 and 1944: most were French models, but 13 also came from Norway after
the German Invasion. The aircraft was well liked by Finnish pilots, who nicknamed it Sussu, or
‘sweetheart’, and they scored a truly remarkable ratio of 190 kills for the loss of just 15.
Some of the Hawks would remain in France to be operated by the Vichy Air Force.
In 1942, during the landings of Operation Torch, elements of these units would engage
carrier-launched Grumman F4F Wildcats. It was one of the few occasions of the war
where American-build aircraft would engage other American-built aircraft. The battle was rather one
sided though, with the Hawks being considerably outclassed by their carrier-based opponents,
and the battle ended with the loss of 15 planes against 7.
After France, England would become the second biggest operator of Hawks – but only as a result
of the additional influx of French models in 1940. Based on several favourable trials,
the British Government briefly entertained the idea of ordering the Hawk for RAF service,
but the order for units was never placed. In some respects, the Hawk turned out to be
superior to the Mk I version of the Spitfire – a statement that is no doubt heresy in some
aviation circles, but it’s true. The RAE observed that in a diving attack at 400mph
the Hawk was Superior to the Spitfire thanks to its lighter and well harmonised controls.
In dogfight conditions at 250mph, again, the Hawk wiped the Spitfire’s eye by being more
manoeuvrable and easier to control… mostly because its elevators – unlike the Spitfires – weren’t
overly sensitive to the point of being a threat to pilot safety. However, the Spitfire won out
thanks to its raw power and acceleration, which allowed its pilots to engage and break from combat
at will, something the Hawk could not achieve. In RAF service the impressed Hawk 75s from France
would be renamed the Mohawk. In total the RAF would find itself in possession of 229 planes,
mostly French, but some also came from the Middle East and India. They were re-designated into four
sub-variants as the Mohawk Mks 1 through to 4. Early on it was decided that they were not
suitable for the European theatre, though a bit of wounded pride from the aforementioned
tests may have influenced this decision, and the Mohawks were sent to South Africa and India.
Five squadrons of Mohawks were operated by South Africa, and two were based in India. At one point,
just eight Mohawks provided the only fighter defence for all of northeast India, being kept
mechanically operational by sheer willpower, and the fighter remained operational on the
Burma front until finally being replaced by more modern fighters – including its
successor, the P-40 – in December 1943. In total, the P-36 would be operated by no
less than 14 different countries – mostly as an export unit, but sometimes as captured equipment.
Records have them being operated by Argentina, Brazil, Britain, China, Finland,
France, India, Iran, The Dutch East Indies, Norway, Peru, Portugal, South Africa,
and Thailand. For an aircraft that started off with an appalling history of mechanical problems,
the P-36 well and truly redeemed itself overseas, and a few models even managed to survive the war.
Several surviving examples can be found around the world, including two airworthy models that
are part of the Fighter Collection in Duxford. For Curtiss the P-36 was a commercial success,
with over 1100 domestic and export models being built. But more importantly, its
development - and the hard lessons learned from it - set a foundation for Curtiss to develop one
of the most important fighter aircraft of world war 2: the P-40 Warhawk…but that’s a video for
another day. As always, thank you all very much for watching, and I’ll catch you all next time.