Complex sentence: After the sinking of the "Ark Royal", Smith returned to Australia, where he was appointed as Liaison Officer to the heavy cruiser USS Chicago until the 1st May, when he was appointed to HMAS "Canberra" as the Observer for aircraft.
Split into simpler sentences: After the sinking of the "Ark Royal", Smith returned to Australia where he was appointed as liaison officer to the United States Navy heavy cruiser USS Chicago. He served in this position until May, when he was appointed to HMAS "Canberra" as the observer for aircraft.