parallel with the fuselage. On 29 February 1940, the Admiralty requested that the Air Ministry formally sanction the production of 50 folding-wing Spitfires, the first of which was to be delivered in July that year. For various reasons, Winston Churchill, who was First Lord of the Admiralty, cancelled the order, writing to Lord Beaverbrook: "I regard it as of very great importance that the production of Fulmars should be kept going". At a time of considerable demand for land-based Spitfires, due to the Fall of France and the subsequent Battle of Britain, the diversion of resources to facilitate the development and manufacture of a naval variant would have naturally reduced Spitfire production. To partially cover the gap until the Fulmar's replacement (Specification N.5/40 – which would be the Fairey Firefly) was able to enter service, it was decided to instead order a number of Grumman Wildcats from America to equip the FAA. These aircraft would enter service towards the end of 1940 as the Martlet. During late 1941 and early 1942, the Admiralty again assessed the Spitfire for possible conversion. In late 1941, a total of 48 Spitfire Mk Vb were converted by Air Training Service Ltd. at Hamble to become "hooked Spitfires". This was the Seafire Mk Ib and would be the first of several Seafire variants to reach the Fleet Air Arm. This version of the Seafire was mainly used to allow the Royal Navy to gain experience in operating the Spitfire on aircraft carriers. The main structural change was made to the lower rear fuselage which incorporated an A-frame style arrestor hook and strengthened lower longerons. It was soon discovered that the fuselage, especially around hatches, was too weak for carrier operations. In an attempt to alleviate this condition, reinforcing strips were riveted around hatch openings and along the main fuselage longerons. A further 118 Seafire Mk Ibs incorporating the fuselage reinforcements were modified from Spitfire Vbs 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 Seafires the instruments were re-calibrated to read kn and nmi rather than mph and mi. The fixed armament was the same as that of the Spitfire Vb; two 20 mm (.79 in) Hispano Mk II cannon with 60 rpg fed from a "drum" magazine and four .303