I was wondering if Short Brothers ever proposed a land based transport using the Short Sunderland or one of its other flying boats as a starting point, with the result being like a smaller version of what Blohm & Voss proposed to do with BV 238 to create the BV 250?
Where is the requirement?
Pre-WW2 most of the bomber specs included requirements for their use as transports. For example:-
Vickers Valentia produced as a bomber transport. Still in service in Middle East in WW2
C.26/31 for a bomber transport. Amongst the loads to be carried 24 fully equipped troops or 10 stretcher cases. Bristol won with the Bombay. Used as transport in WW2 in ME.
29/35 for a Heavy Bomber Development to retain secondary role as a standby transport. Produced the Handley Page Harrow. Used as transport at home in WW2.
B.12/36 that led to the Short Stirling. IIRC this also had a transport requirement.
P.13/36 for a Medium Bomber that led to the Manchester & Halifax. Initially included a requirement to carry 10 fully equipped troops which was finally dropped around 1940.
The successor to the Sunderland was intended to be the Short Shetland produced to Spec R.14/40 and developed in conjunction with Saro, as a flying boat for general recce. Later consideration was given to its use as a transport.
Once the US entered WW2 there was agreement that Britain would concentrate on offensive types, leaving the transport field to the USA. So the only British wartime transport types are leftovers from pre-war or bomber conversions from Stirlings, Halifaxes, Warwicks & Albemarles. Interest in civilian air transport types only begins again with the creation of the Brabazon Committee which held its first meeting in Dec 1942. One of its aims was to arrive at requirements for new types that would not directly compete with US types, so allowing a worldwide market for them. It held its final meeting in Nov 1945. It led to many types of different sizes, some successful, others less so and others failures. one was the Saro Princess flying boat.