Hawker Typhoon

The Hawker Typhoon (Tiffy in RAF slang), was a British single-seat fighter-bomber, produced by Hawker Aircraft. It was designed to be a medium-high altitude interceptor, as a direct replacement for the Hawker Hurricane, but several design problems were encountered, and it never completely satisfied this requirement.

Its service introduction in mid-1941 was plagued with problems, and for several months the aircraft faced a doubtful future. However, when the Luftwaffe brought the formidable Focke-Wulf Fw 190 into service in 1941 the Typhoon was the only RAF fighter capable of catching it at low altitudes; as a result it secured a new role as a low-altitude interceptor.

Through the support of pilots such as Roland Beamont it also established itself in roles such as night-time intruder and a long-range fighter.

From late 1942 the Typhoon was equipped with bombs, and from late 1943 RP-3 ground attack rockets were added to its armoury. Using these two weapons, the Typhoon became one of the Second World War's most successful ground-attack aircraft.

Origins
Even before the new Hurricane was rolling off the production lines in March 1937, Sydney Camm had moved on to designing its replacement. The two preliminary designs were very similar and were larger than the Hurricane. These later became known as the "N" and "R" (from the initial of the engine manufacturers), because they were designed for the newly developed Napier Sabre and Rolls-Royce Vulture engines respectively. Both engines used 24 cylinders and were designed to be able to deliver over 2,000 hp (1,491 kW); the difference between the two was primarily in the arrangement of the cylinders – an H-block in the Sabre and an X-block in the Vulture. Hawker submitted these preliminary designs in July 1937, but were advised to wait until a formal specification for a new fighter was issued.

In March 1938, Hawker received from the Air Ministry Specification F.18/37. F.18/37 asked for a fighter which would be able to achieve at least 400 mph (644 km/h) at 15000 ft and specified a British engine with a two-speed supercharger. The armament fitted was to be twelve Browning machine guns with 500 rounds per gun, with a provision for alternative combinations of weaponry. It was in response to this specification that Camm and his design team started formal development of the designs and construction of the prototypes.

The basic design of the Typhoon was a combination of traditional Hawker and more modern construction techniques; the front fuselage structure, from the engine mountings to the rear of the cockpit, was made up of bolted and welded duralumin or steel tubes, while the rear fuselage was a flush-riveted, semi-monocoque structure. The forward fuselage and cockpit skinning was made up of large, removable duralumin panels, allowing easy external access to the engine and engine accessories and most of the important hydraulic and electrical equipment.

The shallow-angle inverted gull wing had a span of 41 ft, with a wing area of 279 sq ft (29.6 sq m). The airfoil used was a NACA 22 wing section, with a thickness to chord ratio of 19.5% at the root tapering to 12% at the tip. The wing possessed great structural strength, provided plenty of room for fuel tanks and a heavy armament, while allowing the aircraft to be a steady weapons platform. The inner wings, outboard of the fuselage had a 1° anhedral, while the outer wings, attached just outboard of the undercarriage legs, had a dihedral of 5½°. Each of the inner wings incorporated two fuel tanks; the "main" tanks, housed in a bay outboard and to the rear of the main undercarriage bays, had a capacity of 40 gallons; while the "nose" tanks, built into the wing leading edges, forward of the main spar, had a capacity of 37 gallons each. Also incorporated into the inner wings was an undercarriage with a track of 13 ft 6¾ in.

Although the Typhoon was expected to achieve over 400 mph (644 km/h) in level flight at 20,000 ft, the thick wings created a large drag rise and prevented higher speeds than the 410 mph at 20000 ft achieved in tests. The climb rate and performance above that level was also considered disappointing. In addition, when the Typhoon was dived at speeds of over 500 mph (805 km/h), the drag rise resulted in buffeting and trim changes. These compressibility problems led to Camm designing the Typhoon II, later known as the Tempest, which used much thinner wings with a laminar flow section.

Prototypes
The first flight of the first Typhoon prototype, P5212, made by Hawker's Chief test Pilot Philip Lucas from Langley, was delayed until 24 February 1940 because of the problems with the development of the Sabre engine. Although unarmed for its first flights, P5212 later carried an armament of 12 .303 in (7.7 mm) Brownings, set in groups of six in each outer wing panel; this was the armament fitted to the first 110 Typhoons, known as the Typhoon IA. P5212 also had a small tail-fin, triple exhaust stubs and no wheel doors fitted to the centre-section. On 9 May 1940 the prototype suffered from a mid-air structural failure, at the join between the forward fuselage and rear fuselage, just behind the pilot's seat. Philip Lucas could see daylight through the split but, instead of bailing out, he was able to land the stricken Typhoon and was later awarded the George Medal.

On 15 May the Minister of Aircraft Production, Lord Beaverbrook, ordered that resources should be concentrated on the production of five main aircraft types (the Spitfire and Hurricane fighters and the Whitley, Wellington and the Blenheim bombers). As a result development of the Typhoon was slowed, production plans were postponed and test flying continued at a reduced rate.

As a result of the delays the second prototype, P5216, first flew on 3 May 1941: P5216 carried an armament of four belt-fed 20 mm (.79 in) Hispano Mk II cannon, with 140 rounds per gun and was the first prototype of the Typhoon IB series. In the interim between construction of the first and second prototypes, the Air Ministry had given Hawker an instruction to proceed with the construction of 1,000 of the new fighters. It was felt that the Vulture engine was more promising, so the order covered 500 Tornadoes and 250 Typhoons, with the balance to be decided once the two had been compared. It was also decided that because Hawker was dealing with increasing Hurricane production the Tornado would be built by Avro, while Gloster would build the Typhoons at Hucclecote. Avro and Gloster were both aircraft companies within the Hawker Siddeley group. As a result of good progress by Gloster, the first production Typhoon R7576 was first flown on 27 May 1941 by Michael Daunt, just over three weeks after the second prototype.

Introduction
In 1941 the Spitfire Vs which equipped the bulk of Fighter Command squadrons were outclassed in combat with the Focke-Wulf Fw 190 and were suffering heavy losses. The Typhoon was rushed into squadron service (with Nos. 56 and 609 Squadrons) in summer 1941 in an attempt to counter the Fw 190. This decision proved to be a disaster, and several Typhoons were lost to unknown causes. Subsequently, the Air Ministry began to consider halting production of the Typhoon.

In August 1942, Hawker’s second test pilot, Ken Seth-Smith, while deputising for Chief Test Pilot Philip Lucas, was carrying out a straight and level speed test from Langley, Hawker’s test centre. The aircraft broke up over Thorpe, killing the pilot. Sydney Camm and the design team immediately ruled out pilot error which had been suspected in earlier crashes. Intensive investigations revealed that the elevator mass-balance had torn away from the fuselage structure allowing intense flutter to develop, failing the structure and causing the tail to break away. Immediate modifications to the structure, and the control runs, effectively solved the structural problem. (Much earlier Philip Lucas had landed a prototype aircraft with structural failure but this had been due to other failings.) Mod 286 was a partial remedy, although there were still failures right up to the end of the Typhoon's service life. The Sabre engine was also a constant source of problems, notably in colder weather, where it was very difficult to start.

The Typhoon did not begin to mature as a reliable aircraft until the end of 1942, when its good qualities—seen from the start by S/L Roland Beamont of 609 Squadron—became apparent. Beamont had worked as a Hawker production test pilot while resting from operations, and had stayed with Seth-Smith, having his first flight in the aircraft at that time. It was extremely fast, tough and capable, and its unplanned bomb load was doubled and then doubled again. During late 1942 and early 1943, the Typhoon Squadrons on the South Coast were finally effective in countering the Luftwaffe's "tip and run" low-level nuisance raids, shooting down a score or more fighter-bomber Fw 190s.

To counter such attacks, Typhoon squadrons kept at least one pair of aircraft flying continuously on standing patrols over the South coast, with another pair kept at "readiness"; ready to take off within two minutes, throughout daylight hours. These sections of Typhoons flew at 500 feet or lower, with enough height to spot and then intercept the incoming enemy fighter-bombers. These tactics were successful during early 1943. For example, while flying patrols against these "nuisance" raids, No. 486 (NZ) Squadron claimed 11 fighter-bombers shot down during two months.

The first two Messerschmitt Me 210 fighter-bombers to be destroyed over the British Isles fell to the guns of Typhoons in late 1942, and during a daylight raid by the Luftwaffe on London on 20 January 1943, five Fw 190s were destroyed by Typhoons.

As soon as the aircraft entered service it was immediately apparent the profile of the Typhoon resembled a Fw 190 from some angles, and this similarity caused more than one "friendly fire" incident with Allied anti-aircraft units and other fighters. This led to Typhoons being marked up with high visibility black and white stripes under the wings, a precursor of the markings applied to all Allied aircraft on D-Day.

Switch to ground attack
By 1943, the RAF needed a dedicated ground attack fighter more than a "pure" fighter, and the Typhoon was suited to the role. The powerful engine allowed the aircraft to carry a load of up to two 1,000 lb (454 kg) bombs, equal to the light bombers of only a few years earlier. The bomb-equipped aircraft were nicknamed "Bombphoons" and entered service with No. 181 Squadron, formed in September 1942.

From September 1943, Typhoons could also be armed with four "60 lb" RP-3 rockets under each wing. In October 1943, No. 181 Squadron made the first Typhoon rocket strikes. Although the rocket projectiles were inaccurate and took some considerable skill to aim properly and allow for the drop after firing, "the sheer firepower of just one Typhoon was equivalent to a destroyer's broadside." By the end of 1943, 18 rocket-equipped Typhoon squadrons formed the basis of the RAF's Second Tactical Air Force (2nd TAF) ground attack arm in Europe. In theory, the rocket rails and bomb-racks were interchangeable; in practice, to simplify ordnance supply-lines, some 2nd TAF Typhoon squadrons (such as 198 Squadron) used the rockets only, while other squadrons were armed exclusively with bombs.

By the Normandy landings in June 1944, 2 TAF had 18 operational squadrons of Typhoon IBs, while ADGB had a further nine. The aircraft proved itself to be the most effective RAF tactical strike aircraft, both on interdiction raids against communications and transport targets deep in North Western Europe prior to the invasion, and in direct support of the Allied ground forces after D-Day. A system of close liaison with the ground troops was set up by the RAF and army: RAF radio operators in vehicles equipped with VHF R/T travelled with the troops, often close to the front line. In situations where air support was needed, they were able to call up Typhoons operating in a "Cab Rank", which then continuously attacked the targets marked for them (usually by smoke shells fired by mortar or artillery) until they were destroyed.



Against the Wehrmacht's tanks, the rockets needed to hit the thin-walled engine compartment or the tracks to have any chance of destroying or disabling the tank. Analysis of destroyed tanks after the Normandy battle showed a "hit-rate" for the air-fired rockets of only 4%. For example, during Operation Goodwood (18 to 21 July), the 2nd Tactical Air Force claimed 257 tanks destroyed. A total of 222 were claimed by Typhoon pilots using Rocket Projectiles. Once the area was secured analysts could confirm only 10 out of the 456 German AFVs found in the area could be attributed to Typhoons using rocket projectiles.

At Mortain, in the Falaise pocket, a German counter-attack which started on 7 August, threatened Patton's break-out from the beachhead; this counter-attack was repulsed by 2nd Tactical Air Force Typhoons and the 9th USAAF. During the course of the battle, pilots of the 2nd Tactical Air Force and 9th USAAF claimed to have destroyed a combined total of 252 tanks. Only 177 German tanks and assault guns participated in the battle and only 46 were lost – of which 9 were verified as destroyed by Typhoons, 4% of the total claimed.

However, apart from the physical effects, the effects on the morale of the German troops caught up in a Typhoon RP and cannon attack were decisive, with many tanks and vehicles being abandoned, in spite of superficial damage, such that a signal from the German Army's Chief of Staff stated that the attack had been brought to a standstill by 1300 hrs '...due to the employment of fighter-bombers by the enemy, and the absence of our own air-support.' The 20 mm cannon also destroyed a large number of (unarmoured) support vehicles laden with fuel and ammunition for the armoured vehicles. On 10 July at Mortain, flying in support of the US 30th Infantry Division, Typhoons flew 294 sorties in the afternoon that day, firing 2,088 rockets and dropping 80 ST of bombs. They engaged the German formations while the US 9th AF prevented German fighters from intervening. Dwight D. Eisenhower, the Supreme Allied Commander, said of the Typhoons; "The chief credit in smashing the enemy's spearhead, however, must go to the rocket-firing Typhoon aircraft of the Second Tactical Air Force... The result of the strafing was that the enemy attack was effectively brought to a halt, and a threat was turned into a great victory."

Another form of attack carried out by Typhoons were 'Cloak and Dagger' operations, using intelligence sources to target German HQs. One of the most effective of these was carried out on 24 October 1944, when 146 Typhoon Wing attacked a building in Dordrecht where senior members of the German 15th Army staff were meeting; 17 staff officers and 36 other officers were killed, and the operations of the 15th Army were adversely affected for some time afterwards.

On 24 March 1945, over 400 Typhoons were sent on several missions each to suppress German anti-aircraft guns and Wehrmacht resistance to Operation Varsity, the Allied crossing of the Rhine river that involved two full divisions of 16,600 troops and 1,770 gliders sent across the river.

On 3 May 1945, the Cap Arcona, the Thielbek and the Deutschland were sunk in four separate attacks by RAF Hawker Typhoon 1Bs of No. 83 Group RAF, 2nd Tactical Air Force: the first by 184 Squadron, second by 198 Squadron led by Wing Commander John Robert Baldwin, the third by 263 Squadron led by Squadron Leader Martin T.S. Rumbold and the fourth by 197 Squadron led by Squadron Leader K.J. Harding.

The top scoring Typhoon ace was Group Captain John Robert Baldwin (609 Squadron and Commanding Officer 198 Squadron, 146 (Typhoon) Wing and 123 (Typhoon) Wing), who claimed 15 aircraft shot down during 1942–44. Some 246 Axis aircraft were claimed by Typhoon pilots during the war.

Production of the Typhoon, almost entirely by Gloster, was 3,317 machines. Hawker developed an improved version of the Typhoon, the Typhoon II, but the differences between it and the Mk I were so great that it was effectively a different aircraft, thus it was renamed the Tempest.

Once the war in Europe was over, the RAF was quick to remove the aircraft from front line squadrons; by October 1945, the Typhoon was no longer in use as an operational aircraft, with many of the wartime Typhoon units (for example, 198 Squadron) either being disbanded or renumbered.

Captured Typhoons
By 1943, with its change of role to ground attack, the Typhoon was constantly operating over enemy territory: inevitably some flyable examples were to fall into German hands.

The first Typhoon to be flown by the Luftwaffe was EJ956 SA-I of 486 (NZ) Sqn. On 23 March 1943, two aircraft flown by F/O Smith and F/S Mawson were on a "Rhubarb" over France. Just as they were crossing the coast at low altitude, Mawson's Typhoon was hit by light flak. He managed to belly-land in a field near Cany-Barville, but the aircraft was captured before he could destroy it. The Typhoon was repaired and test flown at Rechlin (a German equivalent to RAE Farnborough), and later served as T9+GK with "Zirkus Rosarius". EJ956 overturned and was written off during a forced landing near Meckelfeld, on 10 August 1944.

On 14 February 1944, another Typhoon was captured and later flown in Zirkus Rosarius. JP548 of 174 Squadron, force landed after engine failure near Marigny, France; the pilot, F/O Proddow evaded capture. This Typhoon crashed at Reinsehlen on 29 July 1944, killing Feldwebel Gold.

A third unidentified Typhoon (possibly an aircraft of 1 Squadron) was also thought to have been flown by the Luftwaffe.

Modifications 1941-1945
As was usual with front line Second World War RAF aircraft, the Typhoon was modified and updated regularly, so that a 1945 production example looked quite different from one built in 1941. In the last months of the war, a number of older aircraft were taken out of storage and overhauled, sometimes seeing active service for the first time; for example, R7771 was from one of the first production batches, built in 1942 with the car-door canopy and other early production features. This Typhoon was delivered to, and served on the Fighter Interception Unit in 1942. In February 1945 R7771 was listed as being in front line service on 182 Sqn.; by then it was fitted with a clear-view "bubble" hood, rocket rails and other late series features.

Carbon monoxide seepage
The first problem encountered with the Typhoon after its entry into service was the seepage of carbon monoxide fumes into the cockpit. In an attempt to alleviate this, longer exhaust stubs were fitted in November 1941 ("Mod [modification] 239"), and at about the same time the port (left) cockpit doors were sealed. The Pilot's Notes for the Typhoon recommended that "Unless Mod. No. 239 has been embodied it is most important that oxygen be used at all times as a precaution against carbon monoxide poisoning." Despite the modifications, the problem was never entirely solved, and the standard procedure throughout the war was for Typhoon pilots to use oxygen from engine start-up to engine shut down. In addition to carbon monoxide seepage, pilots were experiencing unpleasantly high cockpit temperatures; eventually a ventilation tube helped alleviate, but did not solve the problem. In addition two small, rear opening vents were added below the port side radio hatch, just below the canopy.

Tail
A major problem, afflicting early production Typhoons in particular, was a series of structural failures leading to loss of the entire tail sections of some aircraft, mainly during high-speed dives. Eventually a combination of factors was identified, including harmonic vibration, which could quickly lead to metal fatigue, and a weak transport joint just forward of the horizontal tail unit. The loss of the tailplane of R7692 (having only 11 hours of flight recorded) on 11 August 1942, in the hands of an experienced test pilot (Seth-Smith), caused a major reassessment which concluded that the failure of the bracket holding the elevator mass balance bell crank linkage had allowed unrestrained flutter which led to structural failure of the fuselage at the transport joint.

Starting in September 1942, a steel strap was fitted internally across the rear fuselage transport joint, although this soon superseded by Mod 286 (modification number 286), in which 20 alloy "fishplates" were riveted externally across the rear fuselage transport joint, while internally some of the rear fuselage frames were strengthened. This was a permanent measure designed to stop in-flight rear fuselage structural failures and was introduced on the production line from the 820th production aircraft; between December 1942 and March 1943, all Typhoons without Mod 286 were taken out of service and modified. Modified balance weight assemblies were fitted from May 1943. Finally the entire unit was completely replaced with a redesigned assembly from August 1944.

Although these modifications reduced the numbers of Typhoons being lost due to tail assembly failure, towards the end of the Typhoon's life there were more tail failures, this time caused by a change to the undercarriage latch mechanism in late 1944; in high-speed flight the undercarriage fairings were pulled into the slipstream, creating an uneven airflow over the elevators and rudder resulting in tailplane and then rear fuselage structural failure. In total 25 aircraft were lost and 23 pilots killed due to tail failures.

Canopy
The Typhoon was first produced with forward-opening side doors (complete with wind-down windows), with a transparent "roof" hinged to open to the left. The first 162 Typhoons featured a built-up metal-skinned fairing behind the pilot's armoured headrest; the mast for the radio aerial protruded through the fairing. From mid- to late 1941 the solid metal aft canopy fairing was replaced with a transparent structure (later nicknamed "The Coffin Hood"), the pilot's head armour plate was modified to a triangular shape and the side cut-outs were fitted with armoured glass; the first production Typhoon to be fitted with this new structure was R7803. All earlier aircraft were quickly withdrawn and modified. From early 1942 a rear-view mirror was mounted in perspex blister moulded into the later "car-door" canopy roofs. This modification was not very successful, because the mirror was subject to vibration. Despite the new canopy structure, the pilot's visibility was still restricted by the heavy frames and the clutter of equipment under the rear canopy; from August 1943, as an interim measure, pending the introduction of the new "bubble" canopy, the aerial mast and its associated bracing was removed and replaced with a whip aerial further back on the rear fuselage.

Starting in January 1943, R8809 was used to test a new, clear, one piece sliding "bubble" canopy and its associated new windscreen structure which had slimmer frames which provided a far superior field of view to the car-door type. From November 1943 all production aircraft, starting with JR333, were to be so fitted. However, the complex modifications required to the fuselage and a long lead time for new components to reach the production line meant that it took some time before the new canopy became standard. In order to have as many Typhoons of 2nd TAF fitted before "Operation Overlord" conversion kits were produced and Gloster, Hawker and Cunliffe-Owen modified older Typhoons still fitted with the car-door canopy.

Long-range fighter and fighter-bomber
From early 1943 the wings were plumbed and adapted to carry cylindrical 45-gallon drop tanks, increasing the Typhoon's range from 690 miles (911 km) to up to 1,090 miles (1,754 km). This enabled Typhoons to range deep into France, the Netherlands and Belgium. Some units, such as 609 Squadron and 198 Squadron, were able to achieve notable success in both air combat and ground attack operations using these long-range Typhoons.

As production continued, the Typhoon's role changed from a low-level interceptor fighter to a fighter bomber; bomb racks capable of carrying 500-lb (227 kg) bombs were being fitted to the wings from October 1942. These were first used operationally by 181 Squadron. By mid-1943, all Typhoons off the production line were capable of carrying bombs. Bigger, solid rubber, grooved "anti-shimmy" tail wheel tyres were introduced in March 1943 on all Typhoons from the 1,001st production aircraft, EK238. The new tyres helped to make heavier, bomb-laden Typhoons more manageable during ground manoeuvres. With the introduction of the bomb racks, small extensions were added to the cannon shell case ejector slots. These allowed the casings to clear bombs or drop tanks suspended from the wing racks. Because of the vulnerability of the Typhoon's liquid cooled engine in the dedicated ground-attack role it had taken on, some 780 lb (354 kg) of armour was added, lining the sides and bottom of the cockpit and engine compartments and the radiator bath.

With the added weight of the bombs and armour, bigger brake discs were fitted to the mainwheels; at first this only applied to "Bombphoons" but eventually all Typhoons used these brakes. After tests conducted in 1943, it was determined that the Typhoon was capable of carrying a 1,000 lb (454 kg) bomb under each wing. With the increased load, it was decided that the extra take-off performance conferred by a four-bladed propeller was an advantage; this led to the adoption of a four-blade propeller unit (de Havilland or Rotol) from early 1944. Coinciding with the new propeller, it was also decided that the larger tailplanes of the Hawker Tempest were to be fitted when tests showed that larger tailplanes improved the handling characteristics of the Typhoon when carrying 1,000-lb (454 kg) bombs. There were, however, problems experienced with oil seal leaks from the new propeller unit as a consequence of which a growing number of Typhoons were held in Maintenance Units (MUs) awaiting the arrival of new seals from the U.S. In addition, some 200 Typhoons were manufactured with the new Tempest tailplanes and the three bladed propeller. A modification programme was inaugurated but it took several months before a majority of operational Typhoons had both the four-bladed propeller and enlarged tailplane.

In June 1943, Hawker fitted a Typhoon with steel "Mark I" rocket rails, four under each wing; trials at the A & AEE and AFDU showed that the combination of the RP-3 rocket and the stable, high-speed platform of the Typhoon was promising. Carrying the eight rails and rockets, it was found that the top speed was reduced by 38 mph (61 km/h), with no adverse handling effects. As a result, the Mk I rails and RP-3s were first fitted to production aircraft of 181 Sqn. in October 1943. At first attempts were made to arm Typhoons with either bombs or rockets depending on requirements. However, it was soon decided that it was easier to specialise squadrons in one weapon or the other. By D-Day, 2nd TAF was able to field 11 RP Typhoon squadrons and seven "Bombphoon" squadrons.

Later in 1944, attempts were made to increase the firepower by "double banking" rockets on each rail, enabling the Typhoon to carry 16 rockets. The problems involved in operating Typhoons from 2nd TAF airstrips meant that this option was never fully utilised, although some Typhoons did fly operationally with 12 rockets, using double-banked rockets on the inner rails. When extra range was required, Typhoons could also operate carrying a drop tank and two rockets outboard of the tank under each wing. From December 1944, aluminium "Mark III" rails, which weighed 240 lb (109 kg) per set, replaced the steel Mk Is (480 lb [218 kg] per set).

In late 1943, Mk III IFF replaced the Mk I and the tailplane tip to fuselage IFF aerials were replaced by a "bayonet" aerial under the wing's centre section. A Rebecca transponder unit was fitted in 1944, with the associated aerial appearing under the centre section.

Once Typhoons started operating from forward landing grounds in Normandy, it was found that the dust clouds stirred up by propeller wash consisted of over 80% of hard, abrasive material which was damaging the Sabre engines; the sleeve valves in particular were subject to excessive wear, and it was calculated that engines would last for three take-offs. As a result a "dome deflector" was designed and manufactured at great speed by Napier, and most Typhoons were fitted with this within a week. In operational service these mushroom-shaped filters, which became red hot, had a propensity for being blown off the air intake at high speed whenever a Sabre engine backfired. They were soon replaced by drum-shaped filters designed by the RAE and Vokes; these had "cuckoo clock" doors in front, which swung open with the pressure changes caused by engine backfires. This standardised filter became Typhoon Mod.420.

At the end of June 1944, a decision was taken to fit as standard tropical air filters, similar to those fitted on the three Typhoons which had been sent to North Africa in 1943. One thousand sets of the filters were to be manufactured and fitted to front line Typhoons as Mod. 421; it was estimated that these could be fitted to all Typhoons on the production lines by the end of September. Research shows that late Typhoons starting in the RB--- series were fitted with the filters, as were some rebuilt aircraft from earlier production batches. Mod. 421 appeared as a streamlined rectangular "hump" just behind the main radiator fairing and between the inner wheel doors.

A small, elongated oval static port appeared on the rear starboard fuselage in late 1944. This was apparently used to more accurately measure the aircraft altitude.

One Typhoon, R8694, was used by Napier for trials with the more powerful Sabre IV, cooled using an annular radiator and driving a four-bladed propeller; the new engine and radiator arrangement required substantial modifications to the forward fuselage and engine bearer structures. Although a maximum speed of 452 mi/h was claimed by Napier, it was decided that the modifications would not be worthwhile, mainly because of the promising development of the Tempest and the disruption to Typhoon production was unproductive.

Sub-variants
In 1943, one Typhoon, R7881 was converted to a prototype night fighter (N.F. Mk. IB), fitted with A.I. (Airborne Interception, i.e., radar) equipment, a special night-flying cockpit and other modifications. Also in 1943, five Typhoons were modified to "Tropical" standard by fitting of an air filter in a fairing behind the main radiator housing. Three underwent trials in Egypt with 451 (RAAF) Squadron during 1943.

The Typhoon FR IB was developed in early 1944 and was used as a tactical reconnaissance fighter. In this version the port inner cannon was removed and three (one forward-facing 14 in and two vertical five-inch) F24 cameras were carried in its place. Few FR IBs were built, and most served with 268 Squadron, starting in July 1944. The aircraft was never popular with the pilots, who preferred the older Mustang Is and IAs, and the inherent engine and airframe vibrations meant that photos were invariably blurred. As a consequence of these problems, the FR IB was phased out in January 1945.

In 1941, Hawker tendered the Hawker P.1009 "Fleet Fighter" in response to specification N.11/40 for a carrier-based fighter. A new centre section was to be fitted, extending the wingspan to over 45 ft (13.7 m), the wings themselves were to swing and fold parallel to the fuselage, with the leading edges pointing upwards. The rear fuselage was to be longer and a vee arrestor hook and associated catapult gear was to be fitted. The design chosen was to result in the postwar Blackburn Firebrand design.

Flight characteristics
Flight Lieutenant Ken Trott flew Typhoons with 197 Squadron and recalled:

"Rather a large aircraft shall we say, for a single-engine fighter. Terrific power. Quite something to control. I liked it from the point of view of speed and being a very stable gun platform. You could come in on a target at 400 mph and the thing was as steady as a rock."

In early March 1943, at Tangmere, the then new Squadron Leader of 486 (NZ) Squadron, Des Scott, flew a Typhoon for the first time:

"She roared, screamed, groaned and whined, but apart from being rather heavy on the controls at high speeds she came through her tests with flying colours...Applying a few degrees of flap we swung on down into the airfield approach, levelled out above the runway and softly eased down on to her two wheels, leaving her tail up until she dropped it of her own accord.

We were soon back in her bay by the dispersal hut, where I turned off the petrol supply cock. After a few moments she ran herself out and with a spit, sob and weary sigh, her great three-bladed propeller came to a stop. So that was it: I was drenched in perspiration and tired out..."

The performance limitations for speed were noted on the pilot's notes, published by the Air Ministry. Indicated airspeed for diving was set at 525 mi/h. The Typhoon could, if needed, be flown at 300 mi/h with the cockpit "hood" open. Flight with undercarriage and flaps down could be made without incident, at the respective speeds of 210 and 155 mi/h. When the aircraft was carrying bombs, the speed could not exceed 400 mph (due to stability problems).

Notes for the management of the fuel system stated that indicated airspeeds (IAS) in excess of 380 mi/h were not advisable when fitted with auxiliary drop tanks. Tanks were jettisoned at about 200 mi/h, but in an emergency, a release at 350 mi/h was permitted. Tanks were to be ejected in straight and level flight only. General flying ability was positive. The maximum climbing rate was 185 mi/h up to 16000 ft reducing speed by 3 mi/h per 1000 ft above this mark. In stability terms, the aircraft was stable "directionally" and "laterally" but slightly unstable longitudinally, except at high speed, when it was just stable. Aileron control was light and effective up to maximum speed, but at very low speed response was sluggish, particularly when carrying ordnance. The elevator control was rather light and could not be used harshly. There was a tendency to "tighten up" in a looping aircraft. If "black out" conditions were accidentally induced in steep turns or aerobatics, the control column was to be pushed forward "firmly".

Stalling speeds were quite low. The typical Typhoon trait, as with most aircraft at the time, was to drop a wing sharply with flaps either up or down. The stalling speeds varied. The various loads depended on external fittings. All-up weight plus two 500 lb bombs (12,155 lb in total) with flaps up could induce a stall at 90–100 mph. With flaps down, stall was initiated at 70–75 mph. Normal all-up weight (11,120 lb) would see stall at 80–90 and 65–70 mph respectively. With all ammunition and nearly all fuel expended (9,600 lb) stall occurred at 75–80 and 65–70 mph.

Operators
Australia, Belgium,  Canada,  New Zealand,  UK

Survivors
Only one complete Hawker Typhoon still survives – serial number MN235 – and it is on display at the RAF Museum in Hendon, North London. It was previously on display at the National Air and Space Museum (NASM) (Smithsonian Institution) before being presented to the museum in commemoration of the RAF's 50th Anniversary in exchange for a Hawker Hurricane. Several other partial air frames are extant: Typhoon Ib EJ922 (Private; Ex-Peter Smith Collection, UK), Typhoon Ia JR505 (Brian Barnes Collection, UK), Typhoon Ib JP843 (Roger Marley Collection, UK), and Typhoon Ib RB396 (Private; but on display at Fort Veldhuis museum, Netherlands).

Two unidentified cockpit sections are on display at the Imperial War Museum, Duxford, and the Jet Age Museum in Gloucester. Finally, four cockpit reconstruction projects are underway privately.

A Hawker Typhoon replica at the Memorial de la Paix at Caen, France, was constructed using some original components.

Memorial
On 9 June 1994, in recognition of the aircraft and crew's role in the liberation of Normandy, a Typhoon memorial was dedicated by Major M. Roland Heudier at Noyers-Bocage, France. Also present at the ceremony were General Yves Paul Ezanno DFC and bar and Squadron Leader Denis Sweeting, both former Squadron Leaders of No. 198 Squadron RAF.