Supermarine  Seafire F.17 (SX137)

Supermarine  Seafire F.17 (SX137)  [@ Fleet Air Arm Museum]

With the outbreak of WW2 the Fleet Air Arm (FAA) found itself chronically short of modern aircraft and was relying on aircraft like Blackburn Rocs and Gloster Sea Gladiators, both of which proved to be woefully inadequate.  A partial solution to the problem of its outdated fighters was found by adapting land-based aircraft like the Hawker Hurricane for carrier operations and in late 1941 it was decided to adapt the Supermarine Spitfire in similar fashion under the name of Seafire.  The name Seafire was arrived at by collapsing the longer name Sea Spitfire.  An "A-frame" arrestor hook fitted Spitfire flew for the first time on the 16th October 1939 and after further discussions with the Admiralty Supermarine submitted a formal drawing of a Spitfire with folding wings and an arrestor hook.  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 the 29th 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 then the First Lord of the Admiralty, stepped in and requested the continued production of Fulmars.  As a result the order was cancelled and it took a further 18 months before the first Seafires were built.

The first semi-navalised variant was the Seafire I which was based on the Spitfire Vb airframe and powered by the Merlin 45/46.  The armament was the same as that of the Spitfire Vb i.e.  two 20 mm Hispano Mk II cannon and four .303 inch Browning machine guns.  In total 166 conversions were under taken and some of the conversions had clipped wings.  In late 1941 the first 48 Spitfire Vbs were converted by Air Training Service Ltd at Hamble to become "hooked Spitfires".  This variant was mainly used to allow the FAA to gain experience in operating the Seafire on aircraft carriers.  It soon became clear that the fuselage, especially around hatches, was too weak for sustained carrier operations.  In an attempt to alleviate this condition, reinforcing strips were riveted around hatch openings and along key points on the main fuselage.  A further 118, incorporating the fuselage reinforcements, were modified by Cunliffe-Owen at Eastleigh and Air Training Service.  These aircraft were equipped with Naval HF radio equipment and IFF equipment as well as a Type 72 homing beacon.  In these and all subsequent airframes the instruments were re-calibrated to read knots and nautical miles rather than mph and miles.  Provision was also made to carry a 30 gallon "slipper" fuel tank under the fuselage.  In fact 801 Squadron operated this variant on board HMS Furious from October 1942 through to September 1944.

Following on was the semi-navalised Seafire II variant and was based on the Spitfire Vc and carried the same armament.  Apart from the fuselage modifications this version incorporated catapult spools and a single slinging lug on either side of the fuselage, just behind the engine bulkhead.  In total 372 (Supermarine 262 and Westland 110) were built (not converted) and was intended for air reconnaissance (FR) role as well as medium and low level altitude fighter (F) roles.  Both the F.II and FR.II were powered by a Merlin 46 while the four-bladed propellor L.II was 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.  Both types of engine drove a four bladed 10 ft 9 in diameter Rotol propeller.  In addition the FR variant also carried two F.24 aerial cameras.

Supermarine  Seafire F.17 (SX137)

Supermarine  Seafire F.17 (SX137)  [@ Fleet Air Arm Museum]

Based upon the Seafire II Supermarine devised manually folding wings for the Seafire III.   This variant became the first true carrier adaptation of the Spitfire design and therefore had no RAF equivalent, although the first 30 Seafire IIIs (Hybrid) (built by Westland) still lacked the folding wings that allowed them to be used on board those FAA carriers that had small aircraft elevators.   Two of the three versions were powered by the Merlin 55 for the fighter (F) and fighter – reconnaissance roles (FR) roles while the Merlin 55M powered the low altitude type.   Most of the improvements that were being incorporated into the Spitfire were also introduced into this variant.  In total 1220 Seafire IIIs were built, 870 by Westland and 350 by Cunliffe Owen.  In 1947 12 Seafire IIIs were stripped of their naval equipment by Supermarine and delivered to the Irish Air Corps.

All subsequent Seafire variants were Griffon powered and all appeared too late to see war service.  Designed to Specification N.4/43 the first to be built was the Griffon VI powered Seafire XV variant which was essentially a fully navalised Spitfire XII.  Six prototypes were built by Supermarine and in total 392 Seafire XVs were built by Cunliffe-Owen and Westland from late 1944.  The Seafire XV entered service with 892 NAS in May 1945.  On the first 50 aircraft manufactured by Cunliffe Owen the A-frame arrestor hook was strengthened to cope with the greater weight but on subsequent Seafire 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.  The final 30 Seafire XVs were built with the blown teardrop cockpit canopy and cut down rear fuselage as introduced on the Spitfire XVI.  Since the Merlin and Griffin engines turned in opposite directions (Merlin – right) the variant exhibited unusual deck handling behaviour, especially on take-off, with the result that it could led sometimes to a collision with the carrier's island.  At full power the slipstream of the propeller often forced the Seafire to swing to starboard even if the rudder was hard over on the opposite lock.  In addition the undercarriage oleo legs was still the same of those of the much lighter Merlin powered Seafire, 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).  In the event of an asymmetric firing of the RATOG (Rocket Assisted Take Off Gear) equipment the swing could be strongly accentuated.  After successful trials in February 1943 RATOG had become a standard fitting available for all Seafires, however, the early Griffon-engine Seafires were not allowed to use RATOG at sea unless they were ranged forward of the first crash barrier on deck.

The next Griffin powered Seafire to appear was the Seafire XVII (Seafire F.17) which was essentially a modified Seafire XV with a clear view canopy and an extra 33 gals of fuel in the rear fuselage.  In the FR.XVII variant two F.24 cameras (1 vertical and 1 oblique) were fitted in place of the extra fuel tank.  The prototype XVII, NS493, was the third Seafire XV to be built and variant was the last Seafire type to remain in naval service and was finally withdrawn from 764 NAS to November 1954.  The most important change was the reinforced main undercarriage which used longer oleos and a lower rebound ratio.  This went some way towards improving the deck handling qualities of the XV, by reducing the tendency of the propeller tips to catch 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 as 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 (as a result of the new undercarriage) and consequently were able to carry heavier underwing loads than the previous Seafire variants.  In total 232 of this variant were built, 212 by Westland and 20 by Cunliffe-Owen.

SX137 was built by Westland Aircraft at Yeovil and entered service with the Fleet Air Arm at RNAS Culham on the 25th September 1945.  After serving at a number of RNAS (Royal Naval Air Station) bases, SX137 went into storage at RNAS Stretton on the 17th March 1950.  Removed from storage on the 11th May 1951 SX137 went on again to be stationed at a number of RNAS bases including time with 1831 NAS at RNAS Stretton from the 18th June 1951 and with 759 NAS at RNAS Culdrose from the 6th November 1951.  Since being “Struck off Charge” on the 6th May 1955 SX137 has spent most of the subsequent years at the Fleet Air Arm museum.

Supermarine  Seafire F.17 (SX137)

Supermarine  Seafire F.17 (SX137)  [@ Fleet Air Arm Museum]

Built to Specification, N.7/44, the Seafire F.17 was followed by the Griffon 60 powered Seafire F.45, of fifty was built at the Castle Bromwich Spitfire factory.  Modified from a Spitfire F.21 prototype by Cunliffe-Owen it featured a "sting" type arrestor hook but no folding swings.  The Seafire F.45 entered service with 778 Squadron in November 1946 and a few were modified to FR standard in March 1947 by fitting two F.24 cameras in the rear fuselage

The Seafire F.46 was a navalized Spitfire F.22 and featured the cut down rear fuselage, a 24 volt electrical system and a teardrop canopy but no folding wings.  In April 1947 a decision was made to replace the Griffon 61s or 64s driving the five bladed Rotol propellers 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.  These two changes completely transformed the handling characteristics of the aircraft by eliminating the powerful swing to starboard.  Supermarine received an order for two hundred F.46s but only 24 were built.  A small number were built to FR.46 standard by the fitting of a single F.24 camera.

The final variants were the Seafire F.47 and FR.47 which incorporated most of the design features of the F.46 and apart from the first four aircraft included hydraulically powered folding wings.  The Seafire 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 Seafire XVII.  Other features unique to the 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 it was never done.  Performance tests showed that the 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 Seafire 46.  The FR.47 was fitted with a single F.24 camera and most of the 90 Seafire 47s were either built or converted to this standard.

The Seafire saw much action in the Mediterranean in the summer of 1943 and in the Pacific in 1945.  The first use of Seafires in sustained carrier operations was during Operation Torch (the British-American invasion of French North Africa in World War II during the North African Campaign) which started on the 8th November 1942.  Joining the British Pacific Fleet late in 1944, Seafires saw most service in the Far East Pacific campaigns, serving with 887 and 894 Squadrons aboard HMS Indefatigable.  Due to their good high altitude performance and lack of ordnance-carrying capabilities (compared to the Grumman Hellcats and Vought 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.  Compared with contemporary Allied carrier aircraft the Seafire II was able to outperform the Japanese Mitsubishi Zero at low altitudes when the two types were tested against each other in World War II.  However aircraft such as the Hellcat and the Corsair, which were designed from the start as naval fighters, were considerably more robust and generally more powerful.  The Seafire 47, operating from HMS Triumph with 800 Squadron, took part in air strikes against terrorists in Malaya and against North Korean forces in the early weeks of the Korean War.  In 1951 the decision was taken to withdraw all Seafires from front-line service.  Although far from suitable for carrier operations because of its narrow-track undercarriage and long nose the Seafire performed well and was used by the Royal Navy Reserve Air Squadrons until 1954.