No delusions of grandeur, nor right/left mixups - just the response to an Operational Requirement starting back in the 1950s, when the RAF AT fleet was in pretty poor shape, given that resource priority for several years had rightly gone to building up the V-Force. The history is laid out in considerable detail in 'Shorts Aircraft Since 1900' by C.H. Barnes.
By 1957 the Air Staff and Shorts had agreed to proceed with a project known as the Britannic, with development costs to be spread over 30 aircraft. Reductions in the Defence budget in 1958 quickly put paid to that plan - but the need for a strategic freighter remained, particularly at a time when there was a need to get missiles and related kit out to Australia for testing. (There are similarities here with the USAF's C-133 that performed very much like the Belfast, also designed very much with moving missiles around.) Eventually an order was placed in 1959 for the SC5/10, later named 'Belfast' - just 10 aircraft for the RAF, with a further 2 aircraft planned by the company for possible civil orders. Shorts tried hard with civvy operators, but no further orders were placed.
The company continued to look at other possibilities. A V/STOL variant with blown flaps etc was apparently proposed for the Beverley replacement OR that was won by the HS 681, cancelled in 1965 along with TSR2, by the first Wilson government. And discussions were held with Lockheed for a variant with the C-141 wings and T-tail, to be powered with 4 RR turbofans - and having flown both aircraft, I'm sure that's the useful airlifter we never had.
Nonetheless, whilst we had it, it was indeed a most useful aircraft for dealing with bulk or oversized loads. For example: a series of flights at close to max zero-fuel weight to move a mix of APCs and Abbott guns out to BAOR; tasking one Belfast for sqn ground equipment on deployments otherwise needing 2 Hercs; moving helos without dismantling the entire rotor head area. There's a Sea King or a Commando - I've forgotten which - inside this one (XR 371) at Shannon in July 1970, en-route to the States for testing:
