The second Short S.23 Empire Flying Boat (the official designation had no hyphen in flying-boat), G-ADHM, was given the Imperial Airways “C-Class” name Caledonia, and was built specifically for the company’s Atlantic routes with extra fuel tanks for extended range. It made its first transatlantic flight, from Foynes in Ireland to Botwood, Newfoundland, on July 5, 1937.

At most stops along Imperial’s routes customers were transferred to and from the aircraft by launch, as seen here as passengers board G-ADUX, named Cassiopeia after the mother of Andromeda in Greek mythology. It was only in April 1938 that a dedicated mooring jetty was constructed at Imperial’s base at Southampton Docks.

The career of G-AETW Calpurnia was comparatively short; having made its first flight at the end of June 1937, it crashed in Lake Habbaniyah during a sandstorm at night on November 27, 1938, Capt Attwood, First Officer Spottiswoode and two passengers being killed. The all-important Christmas mail was rescued, however.

The first C-Class flying-boat, G-ADHL, named Canopus after the pilot of King Menelaus of Sparta’s ship during the Trojan War, made its first flight on July 3, 1936. As delivered to IAL, Canopus had a cruising speed of 165 m.p.h. (265km/h) at 510 h.p. (of 910 h.p. for take-off) and a range of 760 miles (1,220km) at 165 m.p.h. in still air.

Another piece of ingenious engineering applied to the S.23 by Short Bros was the provision of work platforms that folded out from the leading edge of the wing. Engineers were able to service the Pegasus engines from the platforms without the need to beach the flying-boat. Hoists could be mounted on the engine nacelles to remove or install the engines.

Named Ceres after the Roman goddess of agriculture, S.23 G-AETX made its first flight in July 1937, and was used to survey the IAL route from Alexandria in Egypt to Karachi in India (now Pakistan) via Habbaniyah in Iraq and Sharjah in the Persian Gulf two months later. It was destroyed by an explosion while moored at Durban in December 1942.

An IAL promotional item extolling the virtues of “the most comfortable armchairs in the world..."

Another IAL promotional item, this time pointing out the benefits of the promenade deck, providing “plenty of room to walk about”.

The cockpit of the C-Class flying-boat was remarkably spacious with excellent visibility afforded by the generous glazing wrapped around the upper forward fuselage. Stations for captain and first officer were provided side-by-side with dual controls, aft of which were the radio officer’s control panel and an auxiliary power unit.

Imperial paid a great deal of attention to detail in the appointment of the C-Class cabins, and patented its own specialised design for a lightweight reclining chair. At least one still exists and is, at time of press, for sale on a popular online marketplace website!

Promotional photos of passengers enjoying sumptuous levels of comfort were almost certainly taken in a cabin mock-up!

Imperial’s marketing department emphasised the luxury available aboard its C-Class ’boats. This posed photo of relaxed, happy passengers was used on a Senior Service cigarette card entitled “Comfort in the Air”, which read: “It is hard to realise that these happily engrossed people are several thousand feet above the Earth”.

Capella (G-ADUY) came to grief at Batavia on Java in March 1939. The C-Class fleet suffered a remarkable attrition rate, some 19 of the 31 S.23s built being lost to various causes including taxying accidents, crashes and enemy action during the war. Five of the nine S.30s were also lost, along with one of the two S.33s completed.

A beautifully minimalist contemporary Imperial Airways timetable detailing the flying-boat service from the UK to Egypt. Services to Australia and down through Africa both routed through Alexandria in Egypt, via St Nazaire and Marseille in France, Rome and Brindisi in Italy and Athens and Mirabella Bay (Crete) in the Greek islands.

A contemporary colour cutaway illustration of C-Class flying-boat G-AEUA Calypso, used by IAL for promotional purposes. In this illustration, the aircraft is shown with the internal configuration used on the Empire Air Mail Service (EAMS) routes, after IAL deleted the sleeping bunks and moved the Flight Clerk into what had been the smoking cabin.

A trio of typical aircraft operating commercial services in Africa in the 1930s, including two of IAL’s most important landplanes; Handley Page H.P.42E G-AAUE Hadrian (furthest right) and Armstrong Whitworth AW.15 Atalanta G-ABTJ Artemis, behind Wilson Airways’ de Havilland D.H.84 Dragon VP-KBG, at Kisumu in Kenya.