Dewoitine D.520

Background On 13 July 1934, the French Air Force launched a new technical programme, under which the development of improved fighter aircraft to improve upon the Dewoitine D.510, which was yet to enter service at that point but was already considered to be obsolete in the face of rapid advances being made in several European nations. While French aircraft company Dewoitine initially responded with an improved design based on the D.510, designated as the D.513, this quickly proved to be inferior to the in-development Morane-Saulnier M.S.405, a domestic competitor. By this point, official attention was oriented towards the MS.405, which had already been selected for the re-equipment effort. Specification and rivals On 12 January 1937, the A.23 technical programme was launched by the Air Ministry. Other aircraft designed to the same specification included the Morane-Saulnier M.S.450, the Loire-Nieuport 60 (later C.A.O 200), and the Caudron-Renault C.770, none of which either left the drawing board or entered service. Two other concurrent French designs, the Bloch MB.152.01 and Bloch MB.155.C1 series and the Arsenal VG-33 entered service in small numbers with the French Air Force during the Battle of France, but too late to play a significant role. In addition to the lack of a prototype order, Dewoitine was absorbed into the larger Société nationale des constructions aéronautiques du Midi (SNCAM) state-owned manufacturing consortium. As a result of this organisational restricting, along with continued alterations within the French Air Force's established manufacturing programmes, work on the design of the D.520 was suspended throughout much of 1937, and it was not until January 1938 that a small number of draughtsmen started work on the first detailed drawings for the prototype. However, Émile Dewoitine, now the deputy managing director of SNCAM, was keen to proceed with the project and decided to proceed to the detail design drawing phase with the aim of producing a pair of prototypes and a single structural test frame, confident that official interest would be found for the type. Other aerodynamic improvements were made around this time, such as the minor enlargement of the fin and rudder, for greater lateral stability. The major differences between the first prototype and the second and third were the adoption of a new sliding canopy, the fitting of a re-designed and larger tail unit, and longer Oleo-manufactured undercarriage legs; they also omitted the Handley Page slats fitted to the outer wings on 01. During late September 1939, CEMA took charge of the third prototype to conduct armament trials. Overall, flight tests had proceeded successfully, and resulted in the issuing of a contract in March 1939 for 200 production machines to be powered by the newer -31 engine (later replaced by the -45). A contract for an additional 600 aircraft was issued in June, albeit reduced to 510 in July 1939. Production In April 1939, the rate of production of fighter aircraft throughout France was far beneath official expectations. In addition to domestic orders, Poland was interested in acquiring around 160 D.520s in order. The production standard armament was a HS.404 cannon firing through the propeller hub and four belt-fed MAC 1934 M39 machine guns in the wings. As the first batch of D.520s rolled off the production line, they failed acceptance tests due to insufficient top speed and troublesome cooling. Redesigned compressor intakes, a modified cooling circuit and propulsive exhaust pipes proved to be effective remedies of these shortcomings, but as early examples had to be retrofitted with these improvements, the type was not declared combat ready until April 1940, at which point the D.520's operational standards had been defined. In order to speed up the redesign process, a total of four production aircraft were handed back to SNCAM to serve as special test machines. ==Design==

Overview The Dewoitine D.520 was a French fighter aircraft, intended to be a capable contemporary of types such as the Messerschmitt Bf 109 and Supermarine Spitfire. An all-metal structure was used, except for fabric-covered ailerons and tail surfaces. The wing, even if single-spar, was a solid and rigid unit with a secondary spar and many reinforced parts. The inwardly retracting undercarriage had a broad track, and was fitted with wide, low-pressure tyres. The D.520 was designed to be maintained easily with many inspection panels, a rare feature for its time. Recharging the D.520 ammunition was swift and easy; the machine gun magazines required five minutes each and three minutes for the cannon. To fill the machine gun ammunition boxes took 15 minutes, while five minutes were needed to empty it as the cartridges were not expelled. The D.520's cockpit was set well back in the fuselage, aft of the trailing edge of the wings. This gave the pilot good downward visibility, but the long nose in front of him was a drawback when taxiing on the ground. A self-sealing fuel tank with a capacity of was mounted between the engine and cockpit, along with two wing tanks which, combined, carried another , for a total of ; this was considerably more than the contemporary Bf 109E, Spitfire I and early Italian fighters, each with about fuel capacity. The ferry range was from at which, from June 1940, allowed D.520s to escape to North Africa when France fell. The Hispano engine had some advantages over some later engines; for example, its weight was only , compared to the of the Rolls-Royce Merlin III. Development of the engine had not been straightforward, and had delayed production. The -45 drove an electrically operated Ratier Type 1606M three-bladed, , variable-pitch propeller, while D.520s from No. 351 were fitted with the 12Y-49 engine driving a Chauvière type 3918 pneumatically operated propeller, in diameter. By 1940 a version of the 520D was flying with a Rolls-Royce Merlin X engine. Ernest Hives stated that agreement had been reached with the French Government for the manufacture of the Merlin in France. ("The Merlin in perspective" - A Harvey-Bailey -Rolls-Royce Heritage Trust, p130) Fire suppression system The D.520 had a fire-suppression system with a fire extinguisher activated from the cockpit. The engine was started by a simple but effective system, operating with compressed air. A Viet 250 air compressor charged several air bottles (one with a 12-litre capacity, as well as another eight litre tank, three smaller one litre units were matched to the weapons). The 12-litre air bottle was used for the brakes and later, for the Chauvière propeller's constant speed adjustment. The small air bottles provided up to 12 seconds at or 20 seconds at low level, before the Viet air compressor recharged them. The pilot had a complete set of cockpit instruments, and a ten-litre oxygen bottle located in the fuselage just behind his seat, with either a Munerelle or Gourdou oxygen regulator system mounted on the right instrument panel. Equipment included a Radio Industrie Type Rl 537 radio-receiver set, an OPL RX 39 reflector sight (less effective than the Revi system), a height-adjustable seat, and a sliding canopy with large, clear panels. Except over the long nose, the pilot's view was good, since he was seated quite high over the forward fuselage; however, no rear-facing mirrors were fitted. Armament Production-standard armament consisted of a HS.404, which had an ammunition capacity of 60 rounds, firing through the propeller hub, and four belt-fed MAC 1934 M39 machine guns in the wings, with 675 rounds per gun. Flight performance Although employing a modern design philosophy for its time, the D.520 was considered more difficult to fly than the older MS.406. Captain Eric Brown, commanding officer of the Royal Aircraft Establishment's Captured Enemy Aircraft Flight, tested the D.520 at RAE Farnborough, saying that "It was a nasty little brute. Looked beautiful but didn't fly beautifully. Once you get it on the ground, I was told not to leave the controls until it was in the hangar and the engine stopped. You could be taxiing toward the hangar and sit back when suddenly it would go in a right angle." The handling changed according to the amount of fuel carried; using the fuselage tank alone, fuel consumption had no appreciable effect on handling because the tank was at the centre of gravity, but with full wing tanks, directional control was compromised, especially in a dive. The flight controls were well harmonized and the aircraft was easy to control at high speed. The maximum dive speed tested was with no buffeting and excellent stability both in the dive (depending on fuel load) and as a gun platform. ==Operational history==

France Battle of France The Groupe de Chasse I/3 was the first unit to get the D.520, receiving its first aircraft in January 1940. These initial examples were unarmed and used for pilot training. GC II/3, GC III/3, GC III/6 and GC II/7 later completed conversion on the D.520. A naval unit, the 1er Flotille de Chasse, was also equipped with the Dewoitine. However, only GC I/3, II/7, II/6 and the naval AC 1 saw any action in the Battle of France. GC III/7 converted to the D.520 too late to be involved in any action. In addition, several aircraft were flown by non-operational units, such as the special patrol of the École de l'air military school, as well as a handful flown by Polish and civilian pilots in defence of airstrips and production facilities in the vicinity of Toulouse. Eighty five D.520s were lost. By the armistice at the end of June 1940, 437 D.520s had been constructed, 351 of these having been delivered. GC I/3, II/3, III/3, III/6 and II/7 flew their aircraft to Algeria to avoid capture. One of the most successful D.520 pilots was Pierre Le Gloan, who shot 18 aircraft down (four Germans, seven Italian and seven British), scoring all but two of his kills with the D.520, and ranked as the fourth-highest French ace of the war. However, no D.520 units were to be stationed on the French mainland, thus individual aircraft were instead stored or dispatched to units overseas, such as in North Africa. The plan was to have the Dewoitine eventually equip a total of 17 Groupes with 442 aircraft, three escadrilles of the Aéronautique navale with 37 aircraft each, plus three training units with 13 aircraft. The agreement stated that aircraft of this new batch were to be similar to the ones already in service. Even the trip from Rhodes to Syria was . LeO 451s and Martin 167F bombers had few problems, but D.520s were forced to fly a strenuous and dangerous mission, without any help or external assistance. Of the 168 French aircraft (of all types) sent to Syria, 155 accomplished their mission and arrived successfully. The Vichy Air force was numerically strong, but with very few ground crew and spare parts, which meant that the operational flying time for the D.520s was very limited. D.520s of GC III/6 first saw action against British aircraft on 8 June 1941, when they shot down three Fairey Fulmars, losing one D.520 (its pilot was taken prisoner). Over the following days several escort missions were flown to protect Martin, LeO and Bloch 200 (3/39 Esc) bombers from British Royal Navy fighters. Two Hurricanes were shot down (with another D.520 lost) on 9 June. During the Syria campaign, a total of 266 missions were conducted by the Vichy French Air Force: 99 of them were carried out by D.520s, nine by MS.406s, 46 by Martin 167s and 31 by LeO 451s. On 10 July, five D.520s attacked Bristol Blenheim bombers from No. 45 Squadron RAF that were being escorted by seven Curtiss Tomahawks from No. 3 Squadron RAAF (3 Sqn). The French pilots claimed three Blenheims, but at least four of the D.520s were destroyed by the Australian escorts, including two by flying officer Peter Turnbull. The following day, a Dewoitine pilot shot a P-40 down from 3 Sqn, the only Tomahawk lost during the campaign. Other Dewoitine-equipped units in North Africa such as GC II/7 or GC II/3 did not take part in the fighting. Overall, the known D.520 air strength in North Africa was 173 D.520s (143 combat ready) of GC II/3, III/3, III/6, II/7 and II/5; another 30 were in Senegal with GC II/6. The Navy had Esc 1AC and 2AC. Many D.520s were destroyed on the ground by Allied bombing. The French Air Force lost 56 aircraft, among them 13 D.520s. The Navy lost 19 D.520s. Among the 44 kills that the French scored overall, there were five losses from fighters and flak out of a squadron of eight Fairey Albacores from , some of which were shot down by D.520s of GC III/3. Free French Dewoitines A very small number of D.520s were briefly operated by Free French Forces for training purposes. Along with the three examples that had flown to Britain in June 1940, two other Dewoitines were recovered from retreating Vichy forces in Rayak, Lebanon. These D.520s were flown by pilots of the Normandie-Niemen unit before it was sent to the USSR, where they flew the Yakovlev Yak-1 that had many similarities with the French aircraft. With the Allies In December 1942, as French forces formerly under Vichy sided with the Allies, there were 153 D.520s left in French hands in North Africa. Italian pilots appreciated the aircraft's capabilities and Hispano-Suiza HS.404 cannon, at least by 1940–1941 standards. The first three D.520s were assigned to 2° Stormo based at the Turin-Caselle airfield, where they were used for the defence of Turin's industrial area. Other D.520s were captured in Montélimar, Orange, Istres and Aix-en-Provence. (right) with a Regia Aeronautica D.520 At the beginning of 1943, the Italian ace Luigi Gorrini ferried D.520s taken as prizes of war to Italy to be used for defence. "I have collected several dozen Dewoitines from various French airfields and the Toulouse factory", he recalled later. Italian pilots liked the gun, the modern cockpit, the excellent radio set and the easy recovery from a spin but they also complained about the weak undercarriage and the small [cannon] ammunition drum capability; the ammunition was not available in quantities (the HS.404 was not compatible with Breda and Scotti guns, so everything depended on France's depots). At the end of February the 359a Squadriglia (22° Gruppo), led by Major Vittorio Minguzzi, received eight Dewoitine D.520. At that time, American B-24s frequently bombed Naples, so an effective interceptor was badly needed, and D.520s were all that were available in early 1943. The 359a Squadriglia pilots used Dewoitines with some success. On 1 March 1943, Maggiore Minguzzi claimed a B-24 while flying a D.520. This claim was initially only claimed as a probable but was later upgraded to a confirmed. This was probably the first Italian claim using this aircraft. On 21 May 1943, the Regia Aeronautica and the Luftwaffe agreed to exchange 39 Lioré et Olivier LeO 451s, captured by the Italians at the SNCASE factory in Ambérieu-en-Bugey (Lyon), with a stock of 30 D.520s. Subsequently, in the spring and summer of 1943, the Dewoitines were used by 161° Gruppo Autonomo, based in southern Italy with 163a Squadriglia in Grottaglie, 162a Squadriglia in Crotone and 164a Squadriglia in Reggio Calabria. After the armistice of 8 September 1943, three D.520s, previously in service with 24° Gruppo, were used by the Aeronautica Nazionale Repubblicana of the Italian Social Republic for training. The captured Dewoitines were to be delivered to the Axis Balkan Front, although some were used by the Luftwaffe for training purposes while 60 were transferred to Italy and 96, or 120, to the Bulgarian Air Force for use in combat. However, D.520s reached Bulgaria only in August 1943, as the fighter pilots of that country were still training on the type at Nancy with JG 107. The following month, the first 48 Dewoitines were taken over in a ceremony on Karlovo airfield. Two months later, on 24 November, the D.520s were used in combat, when 17 out of the 60 B-24 Liberators of the 15th USAAF arrived over the capital, Sofia, to bomb it. Twenty four Dewoitines took off from Vrazhdebna base (along with 16 Bf 109G-2s from Bojourishte) and attacked the bombers and their 35 escorting P-38 Lightnings. The Bulgarian pilots claimed four American aircraft for the loss of one fighter, three more had to force land. American bombers attacked Sofia again, on 10 December 1943. That day, 31 B-24s escorted by P-38s, were intercepted by six Dewoitines of the II/6th Fighter Regiment from Vrazhdebna and 16 D.520s of the I/6th Fighter Regiment from Karlovo (along with 17 Bf 109G-2s). The Americans claimed 11 D.520s for the loss of only one P-38. The later examination of records showed that only one Dewoitine was lost during that air battle. The Bulgarian Air Force D.520s were again up in force, to face the massive Allied air raid of 30 March 1944. To intercept the 450 bombers (B-17 Flying Fortresses, B-24s and Handley Page Halifaxes) escorted by 150 P-38s, the Bulgarians scrambled 28 Dewoitines from I./6th at Karlovo, six D.520s from II/6th at Vrazhdebna (together with 39 Bf 109G-6s and even Avia 135s). At least ten Allied aircraft (eight bombers and two P-38s) were shot down, while the Bulgarian Air Force lost five fighters and three pilots. Two more Bulgarian aircraft had to force land. During the last Allied raid on Sofia, on 17 April, the II./6th fighter scrambled seven Dewoitines (plus 16 Bf 109s), against 350 B-17s and B-24s escorted by 100 P-51 Mustangs. Bulgarian pilots, who up to that time had encountered only P-38s, mistook the P-51s for their own Bf 109s and before they realized their mistake, seven Bf 109G-6s had been shot down. That day the Bulgarian Air Force suffered the heaviest losses since the beginning of the war: nine fighters shot down and three that had to crash land. Six pilots lost their lives. By 28 September 1944, twenty days after Bulgaria joined the Allies, Dewoitines still equipped an Orlyak (Group) of the 6th Fighter regiment: I Group had a total of 17 D.520s, five under repair and 12 operational, for its three Jato (Squadrons). Numerous sources have mentioned use of the D.520 by the Romanian Air Force, but no evidence has ever been provided. One source claims the so-called Romanian Dewoitines were, in fact, in transit to Bulgaria and only flew over Romania in order to get to their final destination. This seems the most reliable explanation, viewed against the numbers of Dewoitines actually available. Romania did however use the French Bloch MB.150. Postwar service After the war, the D.520s that remained in France were used as trainers; on 1 June 1945, the school base No. 704 was formed at Tours for the purpose of training pilot instructors operating, amongst other types, 17 D.520s. In March 1946, after further experiments, the French Air Force ordered a further batch of 20 D.520s to be likewise converted; however, only 13 of these D.520 DC conversions were completed. The last unit to fly the D.520 was the EPAA (''Équipes de présentation de l'armée de l'air), No. 58. In their final years, the remaining examples were often unserviceable due to general wear and tear. The last flight of an operational D.520 was made on 3 September 1953 with EPAA (Équipes de présentation de l'armée de l'air''). Initially, this unit had flown Yak-3s, formerly of the Normandie-Niemen fighter squadron; these were later replaced with seven D.520s, three of them being two-seaters. ==Variants==

;D.520 :The main production version, sometimes designated the D.520 S (for série – production) or the D.520 C1 (for chasseur – fighter, single-seat). Direct derivatives In 1940, SNCAM had several projects to fit the D.520 airframe with more powerful engines. These developments were halted by the June armistice. ;D.521 :engine replaced by a Rolls-Royce Merlin III, one example was built, but the project was cancelled. ;D.522 :engine replaced by an Allison V-1710 C-1, project abandoned after the armistice (22 June 1940). ;D.523 :engine replaced by slightly different sub-variants of the Hispano-Suiza 12Y-51, with Szydlowski-Planiol supercharger. D.523 Prototype was completing pre-production trials in June 1940. ;D.524 :Version powered by Hispano-Suiza 12Y-89ter engine. One prototype built, but it never flew. ;D.525 :development version of the D.523 ;D.530 :planned version with a Rolls-Royce Merlin or a Hispano-Suiza 12Y. Related prewar projects ;HD.780 :Floatplane derivative of the D.520, one prototype built, but it never flew, the development was cancelled with the armistice. ;D.790 :Carrier-borne derivative project, none built. ;D.550 :Unarmed aircraft built for speed record attempt, with an airframe loosely based on the D.520, but using weight-saving construction techniques. One example was built. ;D.551 and D.552 :Military developments of the D.550. 12 examples were built, but none flew. The development was resumed in 1941, but was quickly terminated by the Germans. Post-armistice developments Several projects were initiated after the June 1940 armistice. They were all terminated with the German occupation of Southern France in November 1942. ;D.520 amélioré :Single production D.520 experimentally fitted with minor improvements to improve top speed with an unchanged engine. ;D.520 Z :D.520 airframe with 12Z engine and minor improvements. One example was built. The development resumed after the war (as SE.520Z), but was eventually cancelled in 1949. ;M.520 T :Different airframe loosely based on the D.520. None built. Postwar derivative ;D.520 DC (double commande – dual control) :Two-seat trainer conversion, at least 13 built. ==Markings==

Apart from the first prototype and postwar examples, D.520s sported the usual French camouflage of dark blue-grey, khaki, and dark brown with light blue-grey undersurfaces. The camouflage pattern was not standardized. National markings were the standard light-blue-white-red roundels on the wingtips, as well as on the rear fuselage, and the rudder flag. Specific markings were applied during the Vichy era, consisting of white outlined fuselage roundels with a white fuselage stripe, and from mid-1941 on, the infamous "slave's pajamas" with red and yellow stripes on the engine cowling and tail surfaces. ==Operators==

Main operators ; • Bulgarian Air Force ; • French Air Force • Aéronautique navale ; • Vichy French Air Force ;: • Free French Air Force ; • Luftwaffe ; • Regia Aeronautica Intended operators ; Royal Romanian Air Force ==Surviving aircraft==

• n°603 – D.520 on display at the ''Conservatoire de l’air et de l’espace d'Aquitaine'' in Bordeaux–Mérignac. • n°650 – D.520 under restoration at the Musée National de la Marine in Rochefort. • n°862 – D.520 on display at the Musée de l’air et de l’espace. It is painted as n°277, which was used by GC III/6 in June 1940. ==Specifications (Dewoitine D.520C.1)==