The Short Mayo Composite Mail Plane.

A unique solution to the problems of long range airmail delivery, proposed by Major Robert H Mayo, Technical General Manager of Imperial Airways, designed and built by the British company Short Brothers before World War II consisted of a 'piggy-back' arrangement of two aircraft.

Mercury annd Maia at Foynes. Photo; National Library of Ireland

The ensemble consisted of a Short S.21 flying boat "Maia" based on the Empire 'C-Class' type already in service carrying, mounted on a trestle, a smaller Short S.20 four engined floatplane "Mercury". With a full payload of 1000 lbs and a maximum fuel load of 1200 imperial gallons Mercury could not get airbourne under her own power but when carried to her operational altitude by Maia, she was capable of crossing the Atlantic unrefueld. Meanwhile Maia was equipped to carry 18 passengers.

Maia's first flight took place on 27th July 1937 and Mercury's on 5th September the same year, on both occasions being flown by Shorts' Chief Test Pilot John Lankester Parker. The first in-flight separation was accomplished on 6th February 1938 with Parker at the controls of Maia and Harold Piper in Mercury near the company's works on the River Medway near Rochester, Kent.

After completing a successful test program the inaugural commercial flight, a transatlantic crossing to Montreal via Foynes in Eire took place on 21st July 1938 with Mercury becoming the first heavier-than-air craft to make a non-stop east to west crossing of the Atlantic. A further record attempt was made in October with a flight from Dundee, Scotland to Alexander Bay in South Africa.

No other examples of the Mayo Composite were built as new types coming into service rendered the concept obsolete and the outbreak of World War Two in September 1939 put an end to its operations. Maia was destroyed in a bombing raid on Poole Harbour and Mercury served for a while with a Free Dutch maritime reconnaissance unit 320 Sqd Royal Air Force before being scrapped to reuse her aluminium for war production.

The video below is a compilation of Movietone News reports on the development and introduction into service of the Mayo Composite.