The matter of a sea-borne Spitfire was raised again in November 1939 when the Air Ministry allowed a Commander Ermen to fly a Spitfire I. After his first flight in R6718 Ermen learned that Joseph Smith, Chief Designer at Supermarine had been instructed to fit an "A-frame" arrestor hook on a Spitfire and that this had flown on 16 October; a drawing of this aircraft had been shown to the FAA on 27 October. After further discussions Supermarine submitted a drawing of a Spitfire with folding wings and an arrestor hook. In this case the wings were designed with a fold just outboard of the undercarriage bays; the outer wings would swivel and fold backwards, parallel with the fuselage. On 29 February 1940 the Admiralty asked the Air Ministry to sanction the production of 50 folding wing Spitfires, with the first deliveries to start in July. However, for various reasons Winston Churchill who was First Lord of the Admiralty stepped in and cancelled the order, writing to Lord Beaverbrook:
It would take over 18 months before the first Seafires were built.
The second semi-navalised variant of the Seafire, and the first to be built as such, was the Seafire F. Mk IIc which was based on the Spitfire Vc. The Vc had several major refinements over the Spitfire Vb. Apart from the modifications included in the main batch of Seafire Ibs this version incorporated catapult spools,and a single slinging lug on either side of the fuselage, just behind the engine bulkhead. Three basic subtypes were produced, the F Mk. IIc and F.R Mk IIc (fighter reconnaissance), powered by a Merlin 46, and the L. Mk IIc powered by a low altitude Merlin 32 specifically manufactured for naval use This version of the Merlin used a "cropped" supercharger impellor to provide greater power at low altitudes than the standard engines; delivering 1,585 hp (1,182 kW) at 2,750 ft (838 m). Both engine models drove a four bladed 10 ft 9 in diameter (3.28 m) Rotol propeller. Because this version used the "C" wing the Hispano cannon were now fed from a 120 round belt magazine, otherwise the armament was the same as that of the Ib; the F.R also carried two F.24 aerial cameras. After trials of Rocket Assisted Take Off Gear or RATOG apparatus (small rocket engines which could be attached to the fuselage or wings of aircraft to help shorten the take-off run) in February 1943, this equipment became a standard fitting available for all Seafires.
The IIc was the first of the Seafires to be deployed operationally in large numbers, with Supermarine building 262 and 110 being built by Westland, who also built 30 Seafire Mk III (Hybrid) (Mk IIIs without folding wings). Although developed for aircraft carrier use, this version still lacked the folding wings needed to allow them to be used on board some Royal Navy carriers, some of which had small aircraft elevators unable to accommodate the full wingspan of the Seafires.
The Seafire F. Mk. III was the first true carrier adaptation of the Spitfire design. It was developed from the Seafire Mk. IIC, but incorporated manually folding wings allowing more of these aircraft to be spotted on deck or in the hangers below. Supermarine devised a system of two straight chordwise folds; a break was introduced immediately outboard of the wheel-wells from which the wing hinged upwards and slightly angled towards the fuselage. A second hinge at each wingtip join allowed the tips to fold down (when the wings were folded the wingtips were folded outwards). This version used the more powerful Merlin 55 (F. Mk. III and F.R. Mk III) or Merlin 55M (L. Mk. III), driving the same four-bladed propeller unit used by the IIC series; the Merlin 55M was another version of the Merlin modified to give maximum performance at low altitude. Other modifications that were made on the Spitfire made their way to the Seafire as well including a slim Aero-Vee air filter and six-stack ejector type exhausts. In addition the shorter barreled, lightweight Hispano Mk V cannon were introduced during production as were overload fuel tank fittings in the wings This Mark was built in larger numbers than any other Seafire variant; of the 1,220 manufactured Westland built 870 and Cunliffe Owen 350. In 1947 12 Mk IIIs were stripped of their naval equipment by Supermarine and delivered to the Irish Air Corps.
After the Mk III series the next Seafire variant to appear was the Seafire F. Mk XV, which was powered by a Griffon VI (single-stage supercharger, rated at 1,850 hp (1,379 kW) at 2,000 ft ) driving a 10 ft 5 in Rotol propeller. Designed in response to Specification N.4/43 this appeared to be a navalised Spitfire F. Mk XII; in reality the Mk XV was an amalgamation of a strengthened Seafire III airframe and wings with the wing fuel tanks, retractable tailwheel, larger elevators and broad-chord "pointed" rudder of the Spitfire VIII. In addition, the engine cowling was different to that of the Spitfire XII series, being secured with a larger number of fasteners and lacking the acorn shaped blister behind the spinner. The final 30 Mk XVs were built with the blown "teardrop" cockpit canopy and cut down rear fuselage introduced on the Spitfire Mk XVI. On the first 50 aircraft manufactured by Cunliffe-Owen a heavier, strengthened A-frame arrestor hook was fitted to cope with the greater weight, On subsequent Mk XVs a new form of "sting" type arrestor hook was used; this version was attached to the reinforced rudder post at the rear of the fuselage and was housed in a fairing below the base of the shortened rudder. A vee-shaped guard forward of the tailwheel prevented arrestor wires getting tangled up with the tailwheel.
390 Seafire XVs were built by Cunliffe-Owen and Westland from late 1944. Six prototypes had been built by Supermarine.
One problem which immediately surfaced was the poor deck behaviour of this mark, especially on take-off. At full power the slipstream of the propeller, which swung to the left (as opposed to the Merlin, which swung to the right), often forced the Spitfire to swing to starboard, even with the rudder hard over on opposite lock. This sometimes led to a collision with the carrier's island. The undercarriage oleo legs were still the same of those of the much lighter Merlin engined Spitfires, meaning that the swing was often accompanied by a series of hops. As an interim measure it was recommended that pilots avoid using full power on take-off (+10 lb "boost" maximum was recommended). There were also problems involved with this swing being strongly accentuated in the event of an asymmetric firing of the RATOG equipment. In the event none of the "first generation" Griffon-engine Seafires were to use RATOG at sea unless they were ranged forward of the first crash barrier on deck.
The Seafire F Mk. XVII was essentially a modified Mk XV; the most important change was the reinforced main undercarriage which used longer oleos and a lower rebound ratio. This went some way towards taming the deck behaviour of the Mk XV, reduced the propensity of the propeller tips "pecking" the deck during an arrested landing, and the softer oleos stopped the aircraft from occasionally bouncing over the arrestor wires and into the crash barrier. Most production XVIIs had the cut down rear fuselage and teardrop canopy (the windscreen was modified to a rounded section, with narrow quarter windows, rather than the flat windscreen used on Spitfires) and an extra 33 gallon fuel tank fitted in the rear fuselage. In addition the wings were reinforced, with a stronger mainspar necessitated by the new undercarriage, and they were able to carry heavier underwing loads than previous Seafire variants. 232 of this variant were built by Westland (212) and Cunliffe-Owen(20).
The Seafire F. and F.R Mk. 45 was the next version of the Seafire to be built, and the first to use a Griffon 60 series engine with a two-stage, two speed supercharger. The prototype TM379 had been modified from a Spitfire F. Mk 21 prototype by Cunliffe-Owen and featured a "sting" type arrestor hook. Because this version was considered to be an "interim" type the wing, which was unchanged from that of the Spitfire 21, was non-folding. The Seafire F. Mk 45 entered service with 778 Squadronin November 1946 and a few were modified to F. R Mk 45s in March 1947 by being fitted with two F.24 cameras in the rear fuselage. Fifty F. Mk 45s were built by the Castle Bromwich factory.
The Seafire F. and F.R Mk. 46 was a Spitfire F. Mk 22 modified to naval standard and featured the cut down rear fuselage and "teardrop" canopy. Again the wing had not been modified to fold. The electrical equipment was changed from using a 12 volt system to one using 24 volts. In April 1947 a decision was made to replace the Griffon 61s or 64s driving a five bladed Rotol propeller unit with Griffon 85s or 87s driving two three bladed Rotol contra-rotating propellers. In addition all but the first few incorporated larger tail units from the Spiteful and Seafang. These two changes completely transformed the handling characteristics of the aircraft by eliminating the powerful swing to starboard of previous Griffon engined variants. Two hundred of the Mk 46s were ordered but only 24 were built, all by Supermarine.
The final version of the Seafire was the Seafire F. and F.R Mk. 47'. There was no true proto type, instead the first production aircraft PS944 and PS945 served as trials aircraft. As the "definitive" carrier based Seafire the Mk 47 incorporated several refinements over earlier variants. After the first four aircraft, with manually folded wings, the Mk 47 incorporated hydraulically powered wing folding, the outer wings folding upwards in one piece, without the folding wingtips of earlier marks. All Mk 47s adopted the Rotl contr-rotating propellers as standard. The Mk 47 also featured a long supercharger air-duct, the intake of which started just behind the spinner, and a modified curved windscreen, similar to that used on the Mk XVII. Other features unique to the Mk 47s were the modified horizontal tail units, which used spring-loaded elevator tabs, a large inertia weight in the elevator control system and beading on the trailing edges of the elevators. These changes improved longitudinal stability, especially when the aircraft was fully loaded. The modified windscreen proved to be unpopular with pilots because of continual problems with misting, and the thicker, repositioned frames obstructed visibility during deck landings. In spite of recommendations to change the windscreen back to a standard Spitfire 24 unit, this was never done. Performance tests showed that the Mk 47 was slightly slower in maximum and climbing speeds, mainly due to the long supercharger air intake, which was less efficient than the shorter type fitted to the Mk 46. The Seafire 47 saw action with 800 Squadron on board HMS Triumph during the Malayan Emergency of 1949 and during the Korean War in 1950. However, in 1951 all Seafires were withdrawn from front-line service. In all 90 F. and F.R Mk 47s were built, all by Supermarine. The last aircraft of the 22,000 of the entire Spitfire/Seafire lineage VR971 left the production line at Supermarine on 28 January 1949.
The Spitfire's original role, and the one at which it proved to be a formidable aircraft was that of short-range land-based interceptor. As a carrier based fighter the design was a compromise and, once in service, suffered from a high attrition rate through structural damage caused by heavy landings on carrier decks: this problem continued even with the stiffening introduced by the Mk II. Also, the Seafire had a narrow undercarriage track, which meant that it was not well suited to deck operations. The many modifications had shifted the centre-of-gravity aft, making low-speed control difficult, and the aircraft's gradual stall characteristics meant that it was difficult to land accurately on the carrier, resulting in a very high accident rate. Other problems included the basic Spitfire's short range and endurance (fine for an interceptor fighter, but not for carrier operation), limited weapons load and that it was dangerous in ditching. The first Seafire variant to overcome many of these problems was the Mk XVII with its new undercarriage design, reinforced structure and extra fuel tanks, although there were still some compromises, and it entered service well after the war was over.
The low point of Seafire operations came during Operation Avalanche the invasion of Salerno in September 1943. Of the 106 Seafires available to the British escort carriers on 9 September only 39 of these were serviceable by the dawn of D-Day plus Two (11 September). Part of this was attributed to flat, calm conditions meaning that there was not enough headwind to stop the "Spitfire float" on landing: many Seafires missed picking up the arrestor wires and flew into the crash barriers while others had their arrestor hooks pulled off the fuselage because they caught the wires at too high a speed. In spite of these problems the Seafire, especially the L. Mk II and III with their low altitude rated Merlin engines found a role as a low to medium altitude interceptor able to protect the RAN carrier fleet.
Compared with other naval fighters, the Seafire II was able to outperform the A6M5 (Zero) at low altitudes when the two types were tested against each other in World War II. Contemporary Allied carrier aircraft which were designed from the ground up as naval fighters, such as the F6F Hellcat and the F4U Corsair, however, were considerably more robust and generally more powerful. The more powerful Seafire III, though, still enjoyed better climb rates and acceleration than these other fighters. Late-war Seafire marks equipped with the Griffon engines enjoyed a considerable increase of performance compared to their Merlin-engined predecessors. However the Griffon powered Seafires had some serious faults. The main problem was a result of the increased power yielded by the Griffon engine; the increase in torque meant the pilot had to continuously correct the flight of the aircraft (to prevent the frame of the aircraft rotating in the other direction to that of the propeller). This was huge problem when attempting to take off and land from an aircraft carrier. The torque also affected the lift of the right wing (the Griffon engines rotated anti-clockwise) which would lose lift and even stall at reasonable speeds. The increased weight of the engine meant that the take-off had to be longer and proved very dangerous from most British carriers. The increased weight of the engine further affected the centre of gravity that Mitchell had concentrated on so carefully in the original Spitfire. As a result the handling of the aircraft suffered. Eventually most of these problems were fixed in Seafire 47 when the 6 bladed contra-rotating propeller was adapted.
The first use of Seafires in sustained carrier operations was Operation Torch. Seafires saw most service in the Far East Pacific campaigns, serving with No. 887 and 894 Squadrons, Fleet Air Arm, aboard HMS Indefatigable and joining the British Pacific Fleet late in 1944. Due to their good high altitude performance and lack of ordnance-carrying capabilities (compared to the Hellcats and Corsairs of the Fleet) the Seafires were allocated the vital defensive duties of Combat Air Patrol (CAP) over the fleet. Seafires were thus heavily involved in countering the Kamikaze attacks during the Iwo Jima landings and beyond. The Seafires' best day was 15 August 1945, shooting down eight attacking aircraft for a single loss. During the campaign 887 NAS claimed 12 kills, and 894 NAS claimed 10 kills (with two more claims earlier in 1944 over Norway).
The top scoring Seafire pilot of the war was Sub-Lieutenant R.H. Reynolds DSC of 894, who claimed 4.5 air victories in 1944–5.
The Irish Air Corps operated Seafires for a time after the war, despite having no naval air service nor aircraft carriers. The aircraft were operated from Baldonnel (Casement Aerodrome) much in the same way as normal Spitfires, but retaining the folding wings. An attempt to recycle the Merlin engines was made in the 1950s, by replacing the ailing Bedford engine in a Churchill tank with an engine from a scrapped Seafire. The project collapsed from lack of funds.
In the Fleet Air Arm, both Spitfires and Seafires were used by a number of squadrons, the Spitfires used by training and land based squadrons. Eleven operational squadrons (800 series) used Spitfires and Seafires (Numbers 801 NAS, 808 NAS, 809 NAS, 879 NAS, 880 NAS, 884 NAS, 885 NAS, 886 NAS, 887 NAS, 897 NAS and 899 NAS)