Hi
Interesting one. It is a great story - but there is a fundamental question of why would approval be given for a squadron to build a prototype rather than a manufacturer. It is an odd situation and I suspect there are probably multiple reasons - Short Brothers' recent failure with the Sunderland IV design, their nationalisation having had a falling out with the Ministry all likely to have played a part in what would be seen as a snub.
From what i've dug out so far, it seems the request came from RAAF - ostensibly in connection to the delivery of Sunderlands to Australia. They didn't want the too overstretched Bristol engines but eyed the P&W enviously. Their experience with the Bristol engines would, obviously, have been from the frontline with 10 and 461 sqns RAAF based in the UK.
That their case was taken up by Coastal Command highlights the concerns the command had with the Bristol engines - and the lengthening delay in the Mk IV which was supposed to be their saviour.
Anyway, I think the core of the story is told in these pages - taken from AIR 2-859 in the National Archives. It is an Air Ministry file of correspondence concerning design and alterations to the Sunderland over quite a long period from 1939 to 1944.





Ok, so if the Air Ministry was told - via Coastal Command - that the RAAF wanted different engines on their Sunderlands and decided they would be of use for the RAF as well, then the question remains, where in the RAAF did the question originate. Did it come from the UK based squadrons and reach Coastal Command via RAAF HQ back home? There may be more in the Australian archives. But this is a start for discussion
AllanK