Messerschmitt Bf.110 in service with the Luftwaffe. Part four. Bf.110 during the Battle of Britain and beyond.

 

This post is a direct continuation of this one:
Messerschmitt Bf.110 in service with the Luftwaffe. Part three. Blitzkrieg on the North & the West.
Barely one year after the beginning of its fighting career, the Bf.110 began to show its defects. After months of mixed results, the concept of the of the Zerstörer had to be seriously rethought, if not discarded entirely.
Just one few weeks after the fall of France, in early July 1940 the Third Reich began with what they considered the final stage of their conquest of Western Europe: the Operation Sealion, codename for the Invasion of England. This was expected to be costly both in men and materiel, it was decided to make sure that the Luftwaffe had the aerial superiority over British skies before the land forces were sent against the south-eastern coast of England. The plan comprised first reducing the sea traffic to nothing in the Channel and the North Sea and then destroying British airfields with massive air raids, employing conventional or dive bombers, under the protection of single-seat or twin-engined fighters.
Taking that into consideration, on 9th July 1940 General Kesselring, commander of Luftflotte 2, whose zone of operations ranged from the Netherlands to Normandy, decided to throw his Zerstörer groups (IE, the Bf.110-equipped units) into the battle for the first time since the Battle of France, with 220 Bf.110Cs being available at that moment. 
On that same day, a naval convoy was spotted entering the Channel so it was decided to intercept it using a large formation of bombers protected by Bf.110Cs. After some chaotical fighting due to bad weather conditions, four the of the Bf.110s were shot down by Royal Air Force's (RAF) Hurricanes.
Even if the loss ratios were not abysmal (the RAF lost the same number of planes during the initial engagements), the Zerstörers failed in their assigned role and showed again how vulnerable they were when they had to face a more manoeuvrable enemy. 
The different Bf.110 units engaged in the Battle of Britain were more or less successful in the many clashes that took place over Sussex and Kent. 
Often at their own cost the Bf.110 pilots had to cope with the shortcomings of their own machines almost on a daily basis, such as sluggish acceleration and low top speed which prevented them from breaking off formation, when necessary to fight. This was emphasized when facing both the Hawker Hurricane and the Supermarine Spitfire.
In order to counter the type less vulnerable, a new tactic was developed over Dunkirk during the closing stages of the Battle of France and was employed to good effect. This consisted on the Bf.110s forming a defensive circle if they were attacked, with the Zerstörers circling in line astern at the same altitude, protecting each other from enemy attacks with both their defensive and offensive weapons. However, this meant that an aircraft designed mainly as an attack plane couldn't perform offensive actions, but defensive one. 
Hermann Göring, the creator of the Zerstörer concept, was personally affected by the initial losses, since his own nephew, Hans-Joachim, a pilot assigned to III./ZG 76 was shot down by Hurricanes on 11th July 1940 over Weymouth Bay.

The Luftwaffe almost succeeded in closing the Channel to all maritime shipping and therefore, moved on to the second phase on the Attack on Britain, called Adlertag (Eagle Day), which took place on 13th August. On that day a massive aerial raid took place, with the Bf.110s claiming approximately thirty kills at the cost of thirteen of their own machines, which made Göring furious. However, the worst day for the Bf.110 during the Battle of Britain was 15th August, when losses topped to thirty planes shot down or damaged beyond repair. Thirty aircraft was the equivalent of a Gruppe for the Luftwaffe. 
To make things worse, three experimented Gruppenkommandeurs (Group Commanders - the equivalent to Wing Commanders in the RAF) were killed during the various engagements when a group of approximately twenty Bf.110D-s based in Norway took part in the attacks; they could be recognized by their extra ventral fuel tank which hampered their manoeuvrability, even if their range was longer. One third of those D-1s which took part in the raid were shot down by British fighters which considered them an easy prey. 
During the following days of August the situation got only worse, specially for ZG 76, the main unit operating Bf.110s as their casualties kept on rising at an unrelenting rate. On 17th August ZG 76 alone lost fifteen machines, totalling 120 machines by the end of the month.
On 18th August Bf.110 activity began to decline for the simple reason that the Luftwaffe couldn't make up the losses they were suffering and the number of available machines was starting to be dangerously low.
Despite all this, Göring, recently promoted to Reichsmarschall, decided to keep the Bf.110s in frontline service by assigning them to missions not suitable for single-engined fighters: those deep inside British territory. With the Luftwaffe still not having enough single-seat fighters, the Bf.110s still available were thrown into the Battle of London, which was part of the second stage of the Battle of Britain, with dramatic results as expected. 
Furthermore, nothing could be done to improve the situation, not even decorating certain Bf.110 unit commanders to boost morale in those seriously beaten units.
On 4th and 27th September a total of fifteen machines were lost, serving with the Erprobungsgruppe 210 (another unit operating the Bf.110), losing on this occasion its third Commanding Officer in as many weeks. When Sealion was finally discarded, 223 out of a total of 237 operational Bf.110s were lost. 
The end of the Battle of Britain sealed the fate of Göring's Zerstörerwaffe concept and the Bf.110 was withdrawn from frontline units, which were either disbanded, just like ZG.2 in October 1940 or sent to the rearguard, like ZG.26 (which lost seven machines on 7th October) or ZG.76.
Just like it happened to the Stuka, the other Luftwaffe icon of the Blitzkrieg, it was decided to send the Bf.110 to the other safer theatres of operations, and the Bf.110 no longer saw daytime combat on the Western Front.

Sources:
1st Histoire & Collections - Avions et Pilotes 11 - Messerschmitt Bf.110 & Me.210-410 1939 -1945

2nd https://en.wikipedia.org/wiki/Messerschmitt_Bf_110_operational_history

Curtiss P-36. Part Eighteen. The P-36 in Pearl Harbor.

 

This is our last post before our summer vacations. See you back later!
The P-36 was delivered to Hawaii in February 1941 on board USS Enterprise (CV-6) aircraft carrier. The Hawks were loaded in California, and then flown off the carrier's deck when the Enterprise was close the shore of Hawaii. This kind of procedure was the first of its kind for the United States Army Air Corps (USAAC) and would later be replicated during World War 2 many times, like during the Siege of Malta, for example. 
This procedure saved considerable time and resources compared to the traditional methos of having the fighters disassembled first, crated and then loaded by crane in a freighter ship, then unloaded and reassembled in Hawaii. 
The only combat action saw by the P-36 in USAAC's markings took place on 7th December 1941, during the bombing of Pearl Harbor. 
During the second wave of Pearl Harbor, amidst the chaos at Wheeler Field, a total of four P-40Cs and two P-36s took off at 8:35 hours in the morning, this was preceded by two P-40s and four P-36 which took off five minutes earlier. One of those who took off flying a P-36 was 2 Lt. Harry W. Brown who took off from Haleiwa auxiliary field and, when headed for Wheeler he soon spotted another P-36 flown by 2 Lt. Bob Rogers and they both managed to shot down a Japanese Nakajima B5N 'Kate' torpedo-bomber of the Imperial Japanese Navy (IJN).  2 Lt. Brown would eventually become an ace and that marked his only aerial victory flying a P-36. After that, he landed back at Haleiwa where the other Curtiss fighters also landed to refuel.
At Wheeler 1 Lt. Lewis Sanders, managed to save many P-36s and got them ready for action. As he was the commander of the 46th Pursuit Squadron, he led four P-36s off at 8:50 am just when the second wave began its attack. One fighter was flown by 2 Lt. Philip Rasmussen who, given the urgence of the situation, had to fly wearing his pyjama and took off in an all-silver P-36A. Among other pilots was 2 Lt. Gordon Sterling who, in the chaos and confusion, manned 2 Lt. Norris' aircraft.
Most of pilots from Wheeler and Haleiwa had just passed their gunnery tests and were, theoretically, better qualified than many other pilots in Hawaii at that time.
In order to gain height advantage Sanders climbed hard for the first 20 minutes of the mission and then he attacked the leading Mitsubishi A6M Zero flown by Lt. Fujita, while 2 Lt. Thacker and Rasmussen were engaged with other IJN fighters. Meanwhile, Sterling managed to get behind another Zero, but got himself in trouble when Fujita's Zero slipped on his tail. Seeing his wingman under fire, Sanders dived on Fujita but couldn't save Sterling who died.
Both Sanders and Sterling were credited with victories, although both Japanese fighters survived, albeit with damage.
While all that combat was taking place, 2. Lt. Thacker experienced a beam attack from a Zero when he was flying in circles trying to re-cock his guns. This attacked damaged his P-36 and the Zero, thought to be flown by P.O. 2c Tanaka, then crossed the nose of 2 Lt. Rasmussen's P-36. In the ensuing fight, the result was uncertain, but Rasmussen remembered to have seen the Zero smoking.
Back at Wheeler, 2 Lt. Bill Haney (future ace) ran to a line of P-36 that were being armed, when the bombs were falling he managed to take off and join Sanders' small ad-hoc group of fighters, only to be struck by friendly anti-air fire coming from the heavy cruiser USS San Francisco. With his engine damaged Haney was forced to land. Just when he landed he sprinted towards another P-36 and took-off only to be hit another friendly anti-air fire which forced him to land again back at Wheeler field. 
When the second wave retreated to the sea, seven P-36s and a pair of P-40s took off to chase them, however they failed to intercept the IJN fighters and flew an uneventful patrol. 
The combat career of the P-36 with the USAAC lasted less than one hour, as the type was outdated and they were quickly replaced by the P-40 Warhawk or other types. By the Battle of Midway in June 1942 the 18th Pursuit Squadron based at Elmendorf Field, Alaska had only three exampled on strength, those being potentially the last American P-36 that saw some frontline action against the Japanese (although they just were employed for uneventful patrols over the southern shore of Alaska), as other USAAF's P-36 were still serving in frontline service, but were based in Panama Canal Zone with the 16th and 32nd Pursuit Groups, but experienced no combat.
During the year 1942 almost every P-36 was relegated to second line duties such as schools or used for mechanics training.

The Curtiss XP-42 was an experimental fighter, developed directly from the P-36. It was powered by a Pratt & Whitney R-1830 Twin Wasp engine and was fitted with a longer and streamlined cowling and a large propeller spinner, in order to improve the aerodynamics of the radial engine.
It flew for the first time in March 1939 and, although faster than the P-36, the P-40 proved to be faster and the new nose arrangement proved to be unresolvable in spite of at least 12 modifications, which eventually resulted in a shorter and less streamlined cowling closely resembling the original P-36. The XP-42 project was cancelled, however the prototype was retained by Curtiss and used as a test bed and was fitted with an all-moving tail. This aircraft was scrapped on 15th July 1947.

Sources:
1st https://en.wikipedia.org/wiki/Curtiss_P-36_Hawk#United_States
2nd Osprey - Aircraf of the Aces 86 - P-36 Hawk Aces of World War II
3rd https://en.wikipedia.org/wiki/Curtiss_XP-42

Curtiss P-36. Part Seventeen.

 

Following with the experimental P-36 variants, the XP-36E was a regular P-36A up-armed with four .30in machine guns plus the two fuselage ones, the XP-36F was armed with two 23 mm (0,91 in) Madsen autocannons placed under the wings, however it was reverted back to regular P-36A's configuration because the cannons created an unacceptable top-speed penalty of just 265 mph (426 km/h).
The XP-36D replaced its fuselage machine guns with two .50 in (12,7 mm) and had four .30 in machine guns in the wings. 
The XP-36B featured an up-rated R-1830-25 engine rated at 1,100 hp which only achieved a top speed of 313 mph (504 km/h), as it was marginally better, it was reverted back to the P-36A. 
All those experimental versions were carried out 1939 and early 1940 and served to test various armament arrangements, however, none of them gave acceptable results and none was fully developed.
The P-36 also received some unusual camouflage scheme. Shown at the Cleveland Air Races in September 1939, and flown by the 27th Pursuit Squadron this scheme consisted on various mix-and-match colours, intended to be disruptive. 

As stated, the P-36 was employed by various Pursuit Groups of the United States Army Air Corps (USAAC), among them 1st Pursuit Group (PG) which employed the type together with the Seversky P-35, until both were replaced by the Republic P-43 Lancer in 1940.
Another unit that the P-36 saw service with was 8th Pursuit Group which, just like 1st PG, employed the P-36 together with the Seversky P-35 during mid-to-late 1930s, which were replaced by the Curtiss P-40 in 1940.
A non-combat unit that employed the P-36 was the 36th Training Group which was activated on 1st February 1940 at Langley Field, Virginia and was initially equipped with the P-36 until being rebased to Puerto Rico in January 1941 and re-equipped with the Bell P-39 Airacobra and the Curtiss P-40.

Sources:
1st https://en.wikipedia.org/wiki/Curtiss_P-36_Hawk
2nd https://en.wikipedia.org/wiki/1st_Operations_Group
3rd https://en.wikipedia.org/wiki/8th_Operations_Group 
4th https://en.wikipedia.org/wiki/36th_Operations_Group
5th Signal Squadron - Aircraft In action 1205 - P-40 Warhawk in Action
6th Histoire & Collections - Avions et Pilotes 3 - Curtiss P-40 & P-36 1939-1945

Curtiss P-36 Hawk. Part sixteen.

 

The Curtiss P-36 is an American fighter of the 1930s that was best known as the predecessor of the P-40 Warhawk. 
Its inception can be traced back to the Curtiss Model 75, which was a private venture by Curtiss, designed by Don R. Berlin, former Northrop's engineer. 
The first prototype, built in 1934 featured an all-metal construction with fabric covered control surfaces and was powered by a Wright XR-1670-5 radial engine yielding 900 hp of power. It was armed with just two machine guns, one .30 in (7,62mm) and one .50 in (12,7mm), firing through the propeller arc. It lacked cockpit armour or self-sealing fuel tanks, as it was typical of the time.
It featured a distinctive landing-gear which rotated 90º to fold the main wheels into the thin trailing portion of the wing, which was a Boeing-patented design for which Curtiss had to pay royalties.
The prototype, flew for the first time on 6th May 1935 and achieved a speed of 281 mph (452 km/h) at 10,000 ft (3,000 m). Later, on 27th May, it was flown to Wright Field, Ohio to take part in the United States Army Air Corps' (USAAC) fly-off for a new single-seat fighter, however, it had to be delayed because Seversky's contender crashed on its way there. 
Taking advantage of this delay, Curtiss replaced the unrealiable Wright XR-1670-5 engine with a Wright XR-1820-39 Cyclone which was 50 hp more powerful. They also reworked the fuselage, adding the scalloped rear windows to improve visibility. The modified prototype was designated as Model 75B and, when powered by the R-1670 engine; Model 75D. It wasn't until April 1936 that the fly-off finally took place with the new engine underperforming, as it failed to deliver its rated power making the aircraft only slightly faster as it could only achieve the speed of 285 mph (459 km/h), marginally better than the initial prototype.
Its main rival , the Seversky P-35 underperformed too and was more expensive to build. Nonetheless it was declared the winner of the contest and was awarded a contract for 77 aircraft. However, the USAAC was concerned about the political situation in Europe and questioned Seversky's production capacity to deliver the P-35s in time, so the sought for a backup fighter. 
The Y1P-36 (company designation: Model 75E), was powered by a Pratt & Whitney R-1830-13 Twin Wasp engine and the scalloped rear canopy was further enlarged. Tests on this prototype yielded so good results that it won the 1937 USAAC competition and was awarded with a production order for 210 P-36A fighters. 

Deliveries began at Wright Field in April 1938 and since its beginning troubles started to show up: exhaust and wing surface problems which increased the aircraft's weight and reduced its top speed. However, once solved, since the aircraft was manoeuvrable, sound, pleasant to fly and easy maintain, the authorities were satisfied. 
It was delivered to the USAAC's Pursuit Groups based in mainland United States and abroad like Hawaii, Puerto Rico and Panama and sold to many other countries.
Soon an improved version, the P-36C was developed. It featured one additional .30 in machine gun installed in each wing, with external ammunition boxes under the. It was powered by a R--1830-17 rated at 1,200 hp of power.

Before production switched to the P-36C, a total of 177 P-36As were manufactured, with the remain of the order, thirty-one being completed as P-36Cs. 
Curtiss also performed various experiments with this new airframe, one of such was the Curtiss H-75J, which featured an improvised external supercharger fitted to starboard side of the plane, the Model 75R which was a regular Model 75A fitted with a R-1830-SC2-G with a turbo-supercharger. This prototype achieved the speed of 330 mph (530 km/h) but it proved to be complex to handle and unreliable. 
Some were tested with a ski undercarriage for winter operations and another one was fitted with the Pratt & Whitney R-1830-31 radial engine, this one was called as Model 75S by the company served as the basis for the Curtiss XP-42 prototype.

One of the first unit to be equipped with the P-36 was 20th Pursuit Group in September 1938, making it their first aircraft with an enclosed cockpit. During this time, this unit took part in training sessions, military manoeuvres and tactical exercises conducting aerial reviews and aircraft demonstrations. They kept their P-36s until September 1940 when they were re-equipped with the P-40.

Sources: 
1st https://en.wikipedia.org/wiki/Curtiss_P-36_Hawk
2nd https://en.wikipedia.org/wiki/Curtiss_XP-42
3rd https://en.wikipedia.org/wiki/20th_Operations_Group
4th Signal Squadron - Aircraft In action 1205 - P-40 Warhawk in Action
5th Histoire & Collections - Avions et Pilotes 3 - Curtiss P-40 & P-36 1939-1945

Curtiss Hawk 75A/Mohawk. Part fifteen. The Hawk in France. Part three.

 

(This post is a direct continuation of the previous one)
Almost one month later of the French armistice that took place on 22nd June 1940, the French Armée de l'Air de l'Armistice (Armistice's Air Force - the official name of Vichy France's Air Force) inventoried all their Curtiss H-75s and so, on 20th July one batch of 45 machines remained in Metropolitan France, while most of them, 186 aircraft, were present in French North Africa, with one hundred being in Morocco, where most of the units that fled just before the armistice. 
The Armée de l'Air de l'Armistice was allowed to have three Curtiss fighter units, those being Groupe de Chasse (GC for short) I/4 at Dakar, French West Africa, GC I/5 at Rabat and GC II/5 at Casablanca, both in Morocco, while GCs II/2 and II/4 were disbanded in August 1940.
Following the two years after the armistice, those units had to affront serious moral crises which forced them to fight against, among others, British troops. During the Battle of Mers-el-Kébir (French Algeria), where the British Royal Navy attacked -and sunk- the remains of the French Fleet based there, GCs I/5 and II/5 managed to get their Hawk 75 airworthy again, as they had been put out of service short after the armistice, to try and fight the Fleet Air Arm aircraft. 
It was during this time that some pilots defected to French Equatorial Africa, which had sided with the General Charles De Gaulle. One of those was Sgt. Marcel Milan who flew his Hawk 75A-3 to Bangui, from Thiès, Senegal in May 1941.
Those two squadrons, GCs I/5 and II/5 also escorted the bombers that took part in the reprisal raid on Gibraltar, following the show of strength at Dakar, during which GC I/4 was also forced to intervene. Their last intervention was in November 1942, during Operation Torch, the Allied landings in Morocco, when the H-75s from GCs I/5 and II/5 clashed against the British Fleet Air Arm and US Navy aircraft. Those combats marked the beginning of the end of the French Hawk 75s, which now they showed their obsolescence, and were becoming more and more difficult to maintain and keep them airworthy due to the lack of spare parts. 
At the end of 1941 it was planned to replace the Hawks in Africa with the French Dewoitine D.520 (probably the best French fighter of World War 2), which were to have been the standard fighter of the pre-war Armée de l'Air. Given that those units equipped with the Morane-Saulnier Ms.406 and the Bloch Mb.152 were given priority, only the second flight of GC II/5 was converted to the D.520 in November 1942 when Germany invaded Vichy France putting an end to the Armée de l'Air de l'Armistice. According to the plan this transition would've been ready for 1943. Sweden showed interest in some of the remaining 76 fighters, out of a total strength of 129, still in service in the fighter groups, but they were sold to Finland. 
The Free French Air Force also employed the Mohawk IV. In September 1941 the Groupe de Chasse 'Alsace' (Alsace Fighter Group) was created with various fighter types, among them the Mohawk IV, which was employed in the training role in the Middle East, as it was outdated for combat role. 
After French Africa rallied to the Allied cause, the surviving Hawks, among them some A-4s powered by the Wright engine, were assigned to training and liaison units. 
Those machines that survived the war were used by the training centre at Cazaux (Ariège - France) where they remained until July 1949, when they were definitely retired from service.

Sources:
1st Histoire & Collections - Avions et Pilotes 7 - French Aircraft from 1939 to 1942 Volume1 Amiot to Curtiss
2nd https://fr.wikipedia.org/wiki/Escadrille_française_de_chasse_n°1 (translated)
3rd https://www.facebook.com/groups/AviationFrancaise1940/posts/3495656893926510/ (translated)
4th AJ-Press - Monografie Lotnicze 61 - Curtiss P-36 Hawk Part 1 (translated)

Curtiss Hawk 75A/Mohawk. Part fourteen. The Hawk in France. Part two.

 

(This post is a direct continuation from the previous one)
The first aircraft of the new contract arrived in France in March 1940 and consisted on more than a hundred Hawks H-75A-3 equipped with the more powerful 1,200 hp Pratt & Whitney R-1830 Twin Wasp SIC3G radial engine. They were quickly assigned to Armée de l'Air (French Air Force) units shortly after arrival. 
During that time, many dozens of H-75s were still on their way at sea, on board cargo ships or even the French aircraft carrier Béarn, which was used as an ad-hoc aircraft cargo ship during that time and not as a pure aircraft carrier. Some of those still-on-sea aircraft were lost to u-boat attacks, while others -those on board of Béarn - were stocked in Antigua, and others were diverted to Casablanca, in Morocco, when France signed the armistice. 
The Hawk H-75A-4, officially called H-751, was powered by a Wright Cyclone R-1820-G205A engine with 1,200 hp at take-off engine and required a different engine cowling shape. This variant was never employed in combat event though it was ordered in large numbers before the armistice. 
In September 1939 four fighter squadrons were equipped with the Curtiss Hawk, those were Groupe de Chasse I/4 II/4, I/5 and II/5. Groupe de Chasse means "Fighter Group" -GC for short- which is the French equivalent to a squadron. All those squadrons were based at Reims and were quickly redeployed to their 'frontline' airfields at Wez-Thuizy, Xaffevilliers, Suippes and Toul-Croix-de-Metz. During the Phoney War the Hawk yielded good results, with a total of 42 kills with 22 more probable ones, at the cost of five pilots and 18 aircraft. Even if it was liked by the pilots, specially for its confort, it had also its flaws, specially its lack of power compared with the most modern enemy aircraft - the Messerschmitt Bf.109-, its weak armament (in the earlier versions which only had four machine guns) and its inadequate armour in the fuel tanks.
During the Battle of France, all the H-75 were active all the time, with a fifth squadron , GC III/2, having been converted from the Morane-Saulnier M.S.406 to the Hawk at the very end of May. Initially they were sent to Belgium to support the ground forces during the initial offensive, but after the 10th June they were chased from one base to another by the German onslaught. During late June all the surviving Hawks started to fall back to French North Africa, crossing the Mediterranean on their own.
At the end of the Battle of France, the Curtiss-equipped units scored more than 300 enemy aircraft, 233 confirmed and 84 probables) for the loss of thirty pilots to combat and accidents. 
Some French pilots acquired their ace status flying the Hawk, like Edmond Marin la Meslée with 16 confirmed kills, Camille Plubeau or Jean Accart, among others, with GC I/5 being the unit with most aces in the 1939-1940 period. 
On the other hand, it is estimated that a hundred or so machines were lost to various reasons such as combat, accidents, destroyed on the ground, etc, being those one third of the delivered machines. 

The Hawk was also employed by the Escadron de Protection de l'usine SNCAC (SNCAC factory protection flight - commonly known as the Bourges factory patrol-) , a fighter unit of the Polish Air Forces in France subordinated to the 1st Fighter Group "Kr". This unit was formed after the 10th May to protect SNCAC factory from bomber raids, with several Polish pilots being assigned there. 
From 16th to 24th May two Polish airmen, Sgt. Jan Kremski and Sgt Waclaw Giermer claimed to have shot down one Heinkel He.111 of 8./KG.51. This patrol saw action again on 5th June when four Polish pilots accompanied by Lt. Marcel Haegelen, chief pilot of SNCAC and an ace from World War 1, took off to intercept He.111s of KG.55. With the assistance of many other French fighters present in the area, several bombers were shot down. One of such kills was awarded to Cne. Bronislaw Kosinski, Lt. Marian Wesolowski and Sgt. Kremski together with Lt. Col. Haegelen shared his twenty-third victory.
(to be concluded)

Sources:
1st Histoire & Collections - Avions et Pilotes 7 - French Aircraft from 1939 to 1942 Volume1 Amiot to Curtiss
2nd https://en.wikipedia.org/wiki/1st_Fighter_Group_(Poland)
3rd https://pl.wikipedia.org/wiki/I_Klucz_Kominowy_(Kr) (translated)
4th Mushroom Model Magazine - Red Series 5112 - Curtiss Hawk H-75 in French Service
5th AJ-Press - Monografie Lotnicze 61 - Curtiss P-36 Hawk Part 1 (translated)

Curtiss Hawk 75A/Mohawk. Part thirteen. The Hawk in France. Part one.

 

In late 1937 the French Conseil Supérieur de l'Air (Air Council - depending of the Ministry of the Air), realised that French aircraft manufacturers alone could not equip the Armée de l'Air (French Air Force) with enough fighters, specially after the objectives of the so-called "Plan V", which was in force at the time, could not be achieved. It was decided therefore to ask for help to foreign manufacturers, so several diplomatic missions were set off, including one to the USSR. With the exception of the Netherlands, from which fifty Koolhoven FK-58 fighters were purchased, no other European country seemed able to supply the desired amount of aircraft in the required period. This made the Conseil to turn their interests towards the United States, where unofficial negotiations were already underway since late 1937 by Baron de la Grange, a personal friend of Presiden Roosevelt. 
The newly appointed Air Minister, Guy la Chambre, set instructions for several hundred of foreign modern fighters to be purchased. Given the short delivery dates the French demanded, the choice was limited to just two fighter models, with very similar performance rates: the Seversky P-35 and the Curtiss H-75. The United States Army Air Corps (USAAC) picked the P-35, so the French turned towards the Curtiss H-75.
Negotiations were specially long an difficult, as the French complained that the unit purchase price was much higher than that of a Morane-Saulnier Ms.406 or a Bloch M.B.152, however, the delays suffered by the French national aircraft industry, together with the deterioration of the European political situation, meant that the Frenchs agreed, and an initial contract for a hundred machines, called H-75A-1 was finally signed in May 1938. These fighters were identical to the P-36A, differing only in being equipped with French equipment such as radio, sights, gauges set in metric system and so on. It was powered by the Pratt & Whitney Twin Wasp R-1830 SC3G radial engine rated at 1,050 hp and had the throttle reversed to comply the general practice of the Armée de l'Air. These machines were armed with four 7.5mm Browning machine guns, two in the engine cowling and two in the wings, built under license in France. 
The prototype of this batch was tested at Buffalo, New York in November 1938 by one of Curtiss' test pilots and later, the first plane intended for France was tested by one pilot of Centre d'Expérimentation du Materiel Aérien (CEMA - Air Equipment Experimental Centre). The machines were dismantled, packed into crates and shipped to le Havre, France, where they arrived on 24th December just to be sent to the SNCAC (Société Nationale de Construction Aéronautique du Centre) at Bourges, which was tasked with re-assembling the Hawks in early 1939.
After the Munich Crisis in September 1938 the international situation deteriorated significantly, and French aircraft manufacturers still could not meet the objectives, so further negotiations were held to purchase the new Curtiss fighter, the H-81 (P-40 Warhawk), however, this project never came into fruition due to delays in the manufacture of the Allison engine it was powered by. Therefore, the Frenchs opted for an improved version of the H-75, which was already foresaw when the first contract was signed.
This improved version featured a reinforced rear fuselage and was powered by a Twin Wasp SG3G radial engine, which was slightly more powerful than its predecessor and, from machine number 141 onwards, was armed with two extra machine guns in the wings, with some older models being retrofitted to this new weapon arrangement. 
These new machines were designated as H-75A-2 and a new order was placed for one hundred more machines.
When the war began in September 1939 all the ordered fighters had already been delivered to the France and were taken in charge by the Armée de l'Air with Groupe de Chasse (GC) I/5, II/5 and I/4 in March and April 1939 being the first ones to be equipped with them. Those squadrons were still equipped with the outdated Dewoitine D.500 or D.501 and were going to be equipped by the new Bloch M.B. 151 and M.B. 152, but their entry into service was being delayed. Those units were followed by GC II/4 which received its new machines in early summer 1939. 
In August 1939 a new French commission was sent to the USA to purchase further new fighters as national production could not still meet the objectives of Plan V, which were expected to achieve the following spring.
In spite of difficult negotiations aggravated by the recent state of war and the declaration of neutrality of the USA, the Frenchs managed to sign a contract - more expensive than the previous ones - in early October 1939 for a total of 535 H-75s, with deliveries taking place over the following year, and one hundred of the new H-81 which was becoming available. Moreover one thousand engines and propellers were also ordered with a production license for the Twin Wasp engine to be manufactured by Talbot-Lago. (To be continued)

Sources:
1st Histoire & Collections - Avions et Pilotes 7 - French Aircraft from 1939 to 1942 Volume1 Amiot to Curtiss
2nd AJ-Press - Monografie Lotnicze 61 - Curtiss P-36 Hawk Part 1