Short Empire S.23M

Two impressed S.23 Mk Is were converted into patrol aircraft: they were fitted with ASV surface-search radar, two Boulton Paul gun turrets and depth charges. In that configuration they received the S.23M designation.

The conversion is no footnote in the type's history. The Empire saw both commercial and military service during the Second World War, on anti-submarine patrols and as a transport, flown by the Royal Air Force, the Royal Australian Air Force and the Royal New Zealand Air Force. The family also had a military sibling from birth, the Short Sunderland, developed in parallel: the S.23M is the reverse case, the civil aircraft taken to the military mission.

When Italy entered the war in June 1940 it became impossible to fly mail between Britain and Egypt — and onward to Australia — via the Mediterranean. The so-called Horseshoe Route was established instead, running from Auckland and Sydney via Cairo to Durban, South Africa, and thence by sea to Britain. After the loss of Singapore in February 1942 it was restricted to the Durban-Calcutta leg.

Wartime experience of operating the type at overload weights showed that the Empires could take off at considerably higher weights than the conservative maxima set by Shorts. The last Empire crossings to America were made in 1940, by Clare and Clyde, but many more flights were made on the long, demanding and vital over-water Lisbon-Bathurst run.