The origin of the Gloster Aircraft Company Gladiator was a private venture modification of the Gloster Gauntlet, developed to meet the requirements of Specification F.7/30, which called for an aircraft capable of at least 250 mph. The prototype that emerged was the single Gloster SS.37 (later allocated serial K5200), which had an open cockpit, whilst later production Gladiator aircraft were fitted with an enclosed, sliding canopy. The aircraft was powered by a Bristol Mercury engine, featuring a clean cantilever undercarriage with internally-sprung Dowty wheels. The SS.37 flew for the first time on 12th September 1934, piloted by Gloster Chief Test Pilot Phillip Edward Gerald 'Gerry' Sayer. During flight testing, it attained a top speed of 242 mph - this left some Ministry officials so sceptical that such a performance level could have been achieved from a radial engine design that they ordered a protracted series of additional tests.
The production aircraft was finally ordered against Specification F.14/35, with 23 aircraft being initially procured, and the type entered RAF service in February 1936. It was then officially designated as Gloster Gladiator I. All manufacturing took place at the Gloster Hucclecote Factory, with the first production aircraft (K6129) being accepted into service on 16th February 1937. The Gloster Gladiator II was similar but made use of a Fairey fixed-pitch three-blade metal propeller. 50 aircraft were ordered in 1938, with many being delivered as Gloster Sea Gladiators. These were then followed by a further order for 300 aircraft divided between Gladiator II and the arrester hook-equipped Sea Gladiator models.
No.72 Squadron at RAF Tangmere were the first RAF unit to be equipped with the Gloster Gladiator and they were soon joined by No.3 Squadron at Kenley, where they replaced their Bristol Bulldogs. The Gloster Gladiator served with considerable distinction during the Second World War, notably in the defence of Malta, in Air Force service in Egypt, and in Norway. A number also formed the spearhead of the RAF London Air Defence Force. No.247 Squadron at RAF Roborough (Devon) also operated Gloster Gladiators during the Battle of Britain, although no combat sorties actually took place due to the high altitude of the aerial dogfights that took place over Kent.
In addition to their use by the RAF, overseas sales of Gladiator I included Latvia (26), Lithuania (14), Belgium (22), China (36), Ireland (4) and Greece (2). Additionally, Norway ordered six Gloster Gladiator I followed by six Gloster Gladiator II whilst Sweden purchased 37 Gloster Gladiator I and 18 Gloster Gladiator II. 30 ex-RAF Gladiator II were supplied to Finland, 17 to Greece and 15 to Portugal. Egypt received 18 ex-RAF Gloster Gladiator I and 27 Gloster Gladiator II, some of which were subsequently taken back into RAF service whilst a single, ex-RAF Gloster Gladiator I, and 11 Gloster Gladiator II aircraft were transferred to the South African Air Force.
The Gloster Gladiator ended its RAF service life in a meteorological role during 1944 and one surviving aircraft (G-AMRK) is currently preserved in flying condition at The Shuttleworth Trust in Bedfordshire.