On Monday 22nd July 1912 Killingholme was on charter to take King George V, Queen Mary and the rest of the royal party to open Immingham Dock.
Killingholme and her sister Brocklesly were brand new that year and had been built for the Hull to New Holland ferry service across the Humber. They were of an unusual design being double ended with rudders at both ends, so that they did not need to turn round while in service, and had particularly tall funnels to increase the natural draught through their boilers thereby doing away with the need for an enclosed boiler room with steam powered fans to force a draught through the boiler.
Killingholme was selected for this special event and was despatched to dry-dock in Grimsby to be painted white for the occasion. Plans to temporarily rename her Queen Mary were thwarted, not by any royal objection, but because the statutory period of notice for such a name change to come into effect had not been given in sufficient time.
On the day the King and Queen boarded Killingholme at the entrance to the lock and gave the signal for the gates to be opened after which Killingholme steamed on into the dock to much cheering from the assembled crowds and music from a brass band.
Killingholme then went alongside the number 2 transit shed where the royal party went ashore and mounted a dais for the speeches during which the King said "I have much pleasure in declaring open Immingham Dock which in future will be known as 'The King's Dock'". He then called for Sam Fay, then General Manager of the Great Central Railway, to come forward to kneel before him and so unexpectedly knighted him on the spot.
After inspecting the guard of honour the King and Queen left by train and Killingholme returned to Hull to take her place once again on the ferry service.