Some Suggestions if I may. No way will Belfast head anywhere, Though Scapa was a fairly bare base in 1939 it had been a fleet base throughout the first world war and their are shore facilities, There is also a radar station, naval air abase and at least one RAF airfield. There is at least one civilian hospital r Kirkwall and medical facilities at the bases on the islands. also there is no way HMS Belfast is heading for the Humber, that is completely nonsensical. If she left Scapa at all she would head for Rosyth in the Firth of Forth. This is a fully equipped Royal naval dockyard and naval base with all the medical facilities required, Edinburgh, with all its hospitals and other facilities is just across the Firth of Forth. This story has an interesting start but I would suggest a little research on RN bases in 1939 and a quick look at some maps! PM me if you wish.
Thank you for the ideas and I will have to pick your brain so to speak.