 The examinations taken by Choules following his training on the "Mercury" qualified him to attend the advanced class on the naval training ship HMS "Impregnable" situated at the Devonport naval base in Plymouth.Choules transferred there on 10 October 1916, for what was to be the final stage of his training before joining the Royal Navy's Grand Fleet.On 20 October 1917, Choules joined the battleship , which was the flagship of the First Battle Squadron and stationed at Scapa Flow in the Orkney Islands.