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| - The first Mk I production machines were ready fairly quickly, with deliveries starting in December 1937. These early aircraft featured fabric-covered wings, and a wooden, two-bladed, fixed-pitch propeller. Initially the tailwheel was designed to be retractable; early on it was discovered that the Hurricane needed a larger rudder area to improve the control characteristics during a spin. To this end the lower part of the rudder was extended and a distinctive ventral "keel" was added to the rear fuselage. The tailwheel was now fixed. Early Hurricanes lacked armour or self-sealing tanks. They used "ring and bead" gunsights, with the ring being mounted above the instrument panel and the bead mounted on a post above the engine cowling. The standard GM2 reflector gunsight was introduced in mid-1939, although many Hurricanes retained the "bead". Fuel capacity was 97 Imperial gal (441 l) in two fuel tanks, each of 34.5 gal (157 l) in the wing centre-section, between the spars; the fuel was pumped from these into a reserve gravity-feed tank which held an additional 28 gal (127 l) in the forward fuselage, just ahead of the cockpit. This was the main fuel feed to the engine. The 7 gal (32 l) oil tank was built into the forward, port centre section. Early "K" serialled Mk Is were powered by the 1,029 hp (768 kW) Rolls-Royce Merlin C engine; from the "L" serial numbers the later Merlin II of 1,030 hp (768 kW) was installed. The main coolant radiator was housed in a fairing under the rear wing centre-section; the oil cooler was also incorporated into the main radiator. The aircraft handling qualities during take-off and landings were excellent due to a wide-track undercarriage with relatively wide low-pressure tyres. Because of this wide, stable platform the Hurricane was an easier aircraft to land, with less fear of nose-overs or "ground-loops" than its RAF Fighter Command counterpart the Supermarine Spitfire. During its operational life the Hurricane was able to operate from all sorts of adverse airfield surfaces with ease. In flight the large, thick wing meant that the fighter proved to be a stable gun platform. It was armed with eight .303 in (7.7 mm) Browning machine guns. The armament was arranged in two lots of four in large gunbays incorporated into the outer wing panels. In 1937 this firepower was enough to outgun the early marks of German Messerschmitt Bf 109, which were equipped with only four light machine guns. By the time of the Battle of Britain, however, it was recognised that this relatively small-calibre armament was inadequate; during the Battle of Britain it was relatively common for Luftwaffe aircraft to survive numerous hits from .303 in (7.7 mm) bullets and still return safely to base. Later versions of the Hurricane were equipped with a more powerful arms package, initially 12 .303 in (7.7 mm) Brownings, and later four 20 mm (.79 in) Hispano cannon. Hurricanes built under license by SABCA in Belgium featured four 12.7 mm (.50 in) FN-Browning guns instead of the .303 inch armament. Hurricane MkI (Mid-late production) In 1939, several changes were made to the Hurricane. The powerplant was changed to the Merlin III driving a de Havilland or Rotol constant speed metal propeller. Ejector exhaust stacks were fitted for added thrust. The fabric covered wings were replaced by re-stressed metal-covered wings. An armour-glass panel was incorporated on the front of the windscreen. The "rod" aerial mast was replaced by a streamlined, tapered design. From about May 1940 70 pounds of armour plate protection was added in the form of head and back armour. Starting in September 1940, IFF equipment was installed. This weighed about 40 lb (18 kg) and could be identified by wire aerials strung between the tailplane tips and rear fuselage. Although the added weight and the aerials reduced maximum speed by about 2 mph (3 km/h), it allowed the aircraft to be identified as "friendly" on radar: lack of such equipment was a factor leading to the Battle of Barking Creek. At about the same time new VHF T/R Type 1133 radios started replacing the HF TR9 sets. The pilots enjoyed a much clearer reception which was a big advantage with the adoption of Wing formations throughout the RAF in 1941. The new installation meant that the wire running between the aerial mast and rudder could be removed, as could the triangular "prong" on the mast. At the start of the war the engine ran on the then-standard 87 octane aviation spirit. From March 1940 increasing quantities of 100 octane fuel, imported from the U.S., became available. This meant that during the defensive battles over Dunkirk the Hurricane Is benefited from an allowable increase in supercharger "boost" from 6 lb to 12 lb without damaging the engine. With the 12 lb "emergency boost", the Merlin III was able to generate 1,305 hp (973 kW) in a five minute burst. If the pilot resorted to emergency boost, he had to report this on landing and it had to be noted in the engine log book. In 1939, the RAF had taken on about 500 of this later design to form the backbone of the fighter squadrons during the Battle of France and into the Battle of Britain. The first RAF ace of the war, a young New Zealander known as "Cobber" Kain, flew a Hurricane with No. 73 Squadron. In June 1940, another wartime ace, Douglas Bader, was promoted to Squadron Leader and took command of No. 242 (Canadian) Squadron flying Hurricane Mk Is. The famous children's author Roald Dahl also flew Hurricanes with No. 80 Squadron in Greece and later in Syria, against the Germans and Vichy France. Although some of the basic design elements of the aircraft were from an earlier generation, the Hurricane proved to be a match, to an extent, for the Luftwaffe's Messerschmitt Bf 109E. In his book, Duel of Eagles, British ace Peter Townsend, who flew Hurricanes with No. 85 Squadron RAF during the Battle of Britain, provides examples demonstrating how the Hurricane's superior turning ability could offset the Bf 109's higher speed. This small turning circle often allowed a well flown Hurricane to get onto the tail of a 109 even more quickly than a Spitfire, assuming a 109 pilot was unwise enough to be lured into a turning match. Against the Hurricane was the aircraft's relatively slow acceleration and a top speed some 10-30 mph (16–48 km/h) slower, depending on altitude. This meant that the 109 pilot often held the initiative when it came to breaking off or attacking during combat. At higher altitudes especially, the Hurricane was hard-pressed to keep up with a well flown 109, or even a Bf 110. Lower down the situation was a little more even. The Rolls-Royce Merlin engine gave more power at low altitude than the Daimler-Benz DB 601 used in the Bf 109, on account of a different supercharger design. The DB601A-1 did not start to outperform the Merlin III and XII until above 15,000 ft (4,572 m). The Merlin's only major drawback was a tendency to cut out during negative-g manoeuvres and inverted flight, on account of fuel starvation from the carburettor. This was temporarily fixed with "Miss Shilling's orifice", a simple modification. A direct- injection carburettor later solved the problem and eventually some versions of the Merlin used direct fuel injection. When attacking Luftwaffe bombers, it was discovered that the Hurricane's fuel tanks were vulnerable to defensive machine gun fire. The greatest hazard was with the unprotected gravity-feed fuel tank in front of the cockpit which could rupture when hit, allowing a jet of flame to penetrate the cockpit through the instrument panel, causing serious burn injuries to the pilot. The wooden and fabric rear fuselage was also far more likely to catch fire than the metal fuselages of its contemporaries. This issue was of such concern to Air Vice Marshal Hugh Dowding that he had Hawker retrofit the fuselage tanks of Hurricanes with a fire-resistant material called "Linatex" as a matter of priority. The wing tanks had already been fitted with a covering of this sealant, but the fuselage tank was considered to be too small a target. Hurricanes were soon being modified at the rate of 75 per month. In one month of combat, 10 July 1940 to 11 August, defensive fire from bombers hit 25 Hurricanes and 25 Spitfires; as a result 11 Hurricanes were shot down compared with two Spitfires. The biggest advantages of the Hurricane were that it was a relatively easy aircraft to fly, which was a boon when it came to squadrons being flooded with inexperienced pilots, and it was a steady gun platform. The closely grouped .303 in (7.7 mm) Brownings created a superior pattern of fire to those of the Spitfire, which were spaced out along the wings, and the armament was more quickly serviced. In spite of its vulnerabilities during the Battle of Britain, the Hurricane shot down the majority of the planes claimed by the RAF (1,593 out of 2,739 in total). Hurricane fighters were sometimes directed against slower bombers whilst the Spitfires attacked German fighters. By the close of the Battle of Britain in late 1940, production of the Spitfire had increased to the point where all squadrons could be supplied with them. In June 1940, the first Hurricane Mk I "Tropical" versions appeared. These featured a Vokes air filter in a large "chin" fairing under the engine cowling. Many of these aircraft were ferried to North Africa and Malta via France and the Mediterranean using fixed, cylindrical 40 gallon fuel tanks under each wing to extend the range. The tropical filter and fuel tanks were to be used on later variants of the Hurricane.
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