HMS K3 was the lead ship of the British K class submarines. She was laid down on 21 May 1915 by Vickers, Barrow-in-Furness. She was commissioned on 4 August 1916. In December 1916, K3, with the future King George VI aboard, uncontrollably dived. The ship plunged to 150 feet with the stern and propellers raised above the waves. It took twenty minutes to free the ship from the sea bed mud and surface successfully. K3 was sold on 26 October 1921 in London.