Following his recovery, Liddell travelled to Canada to complete a course at the Central Navigation School and became a pilot officer navigator. While on leave, he was used as a substitute by the Toronto Scottish under an assumed name and scored twice in a semi-final play-off. He was recalled to Moncton, New Brunswick, before the final. After some seven months in Canada, Liddell returned to Britain and, when based in Perth in 1944, accepted an offer to guest for his boyhood favourites Dunfermline Athletic. He subsequently moved to Northern Ireland for further training, where he declined an offer from former Liverpool goalkeeper Elisha Scott to guest for Belfast Celtic because of a prior agreement to play for Linfield. By the end of the war, Liddell had been assigned to 617 Squadron, helping to transport Allied soldiers back to Britain on leave from Italy.