By comparison with the company's large and cumbersome biplane flying-boats, the Short S.23 of 1936 showed a complete change of style. With four 920 hp (686 kW) Bristol Pegasus XC radial engines, a high-set cantilever monoplane wing, and a streamlined hull, and of all-metal construction, the S.23 had a maximum speed of 200 mph (322 km/h), which was 26 mph (42 km/h) faster than the RAF's contemporary Bristol Bulldog fighter. Such was its promise that Imperial Airways placed an order for 28, for airmail had again taken a hand in aircraft procurement when the British government announced that all first-class mail to the Empire would be carried by air, and these machines were to become known also as Empire or 'C' class flying-boats.

The first S.23 'Canopus' flew from Rochester in July 1936, entering service at the beginning of September, and as further aircraft became available at the rate of about one aircraft every two weeks, they joined the fleet. Operating from the new Imperial Airways flying-boat base at Hythe they were used on services to Australia, Bermuda, Durban, Egypt, Malaya, New York, and East and South Africa.

Original accommodation was for 3,000 lb (1361 kg) of mail and 24 passengers by day or 16 by night, but an increase of 1,000 lb (454 kg) in mail load reduced the passenger capacity to 17. Transatlantic trials made in 1937 without payload, proved the S.23 could not carry an economic payload over the distance, leading to the Short-Mayo Composite, and trials were also conducted with in-flight-refuelling using the Armstrong Whitworth 23 as a tanker. The success of this latter system secured a contract for Flight Refuelling Ltd, which used four Handley Page Harrow tankers to achieve 16 successful flight-refuelled transatlantic crossings before the outbreak of war stopped further development. Short S.30 aircraft powered by 890 hp (664 kW) Bristol Perseus XIIC engines and with more than double the range of the S.23 were used for the transatlantic trials; last variant was the S.33 with 920 hp (686 kW) Bristol Pegasus XCs. Total production of the Empire flying-boats reached 42, of which 31 were S.23s, nine S.30s and two S.33s, construction of a third S.33 being abandoned.

Several S.23s were impressed for RAF service (two of them being modified to S.23M standard with ASV radar and an armament of two four-gun turrets and six depth charges), and a total of 13 Empire 'boats survived the war, by then with 1,010 hp (753 kW) Bristol Pegasus engines; the last, in service with Qantas, was retired in 1947. Shorts also constructed three Short S.26 'boats ordered by Imperial Airways for nonstop transatlantic mail services. Larger than the 'C' class and with 1,380 hp (1029 kW) Bristol Hercules engines, the first 'Golden Hind' was launched in June 1939. Known as the 'G' class, all were impressed for reconnaissance use; one was lost through engine failure but in 1942 the other two were returned to the airline, by then renamed BOAC. One was destroyed in a fatal crash at Lisbon in 1943, and the other survived until it sank during a gale in May 1954.

Power Plant: Four 1,400 h.p. Bristol Hercules
Span: 134 ft 4 in
Length: 101 ft 4 in (later 103 ft 2 in)
Weight (All-Up): 74,500 lb
Max Speed: 209 m.p.h.
Range: 3,200 miles
Crew: 7
Passengers: 38