Short Empire S.23 Mk I

During the 1930s Imperial Airways sought to extend air service across the whole British Empire. Its technical adviser drew up a specification for an aircraft able to carry twenty-four passengers in comfort, plus mail or freight, at a cruising speed of 270 km/h, with a normal range of at least 1,100 km and the capability to extend it to 3,200 km to cross the North Atlantic. It was determined that only a flying boat could meet it.

Short Brothers, which had already built large flying boats for Imperial Airways and the RAF, was the front runner. The company was reluctant to build straight from the drawing board without a prototype, but Imperial Airways rejected the objection: it urgently needed to replace obsolete types. In 1935 the airline announced an order for twenty-eight flying boats of an as-yet undesigned type, weighing eighteen tonnes each. The British press called it one of the world's boldest experiments in aviation.

The team led by Arthur Gouge solved the propeller-to-water clearance problem by putting the wing as high as feasible. The initial idea was to mount it on a hump, as on the Martin M-130, but the fuselage height was increased instead: it gave more internal volume than required and allowed a lighter, stronger integration of the cantilever wing.

After water tank experiments a simplified-vee planing bottom with a far higher length-to-beam ratio than was common was chosen. The aerodynamic and hydrodynamic properties were tested on the smaller Short Scion Senior floatplane, which served as a half-scale prototype for the Empire and its military sibling, the Short Sunderland. Shorts developed its own machinery to produce the T-shaped Hiduminium alloy sections of the main spar, and patented a flap of its own — the Gouge flap — which raised the wing's lift coefficient by 30 per cent and cut landing speed by 12 per cent with only a small drag increase and no trim changes.

The first Empire built, registered G-ADHL and named Canopus, made its first flight in July 1936 with Shorts' chief test pilot John Lankester Parker at the controls. Early flights were relatively trouble-free. On 17 September it first flew for Imperial Airways and the final proving flight, to Marseille, took place on 22 October 1936.

From September 1936 one aircraft was produced per month, with delivery typically occurring right after the first flight. Imperial Airways officially called the type the C-class and gave each of its aircraft a name beginning with C. On 8 February 1937 Castor made the first scheduled flight, from Calshot in Hampshire to Alexandria, covering roughly 3,700 km non-stop.

On 26 February 1938 the final three Empires of the initial order — Coorong, Coogee and Corio — were diverted from Imperial Airways to the Anglo-Australian Qantas Empire Airways. In late 1937 Imperial Airways had placed a follow-on order for eleven more; combined with the original twenty-eight, it was the largest single-customer order for a British civil aircraft to that date. Shorts' Rochester factory produced all the Empires.