I believe the salvage vessel was not allowed by the navy to attempt putting an airline onto the sub. Even tho they had experts on board that had been involved with the salvaging of the german battleships in Scapa Flow.... My father was one of the team there .
I believe that one of the rescue vessels large enough to do the job happened to be coalfired and was a day or so away from Liverpool Bay. Unfortunately, and although it was wartime, her journey was delayed for some time due to local industrial action and refusal to coal her for the journey to Liverpool. When it was sorted however it was too late. Most of the people of Liverpool when I was a child knew of the tragedy.