HMS L4 was built by Vickers, Barrow. She was laid down on 21 June 1916 and was commissioned on 26 December 1918. She sailed with the Submarine Depot Ship HMS Ambrose (1903) to Hong Kong in 1919 as part of the 4th Submarine Flotilla, arriving there in January 1920. On 20 October 1927 off Hong Kong, L4 and HMS L5 rescued crew of the merchant ship SS Irene from a pirate attack after firing her deck gun. HMS L4 was sold on 24 February 1934 and then broken up in Charlestown, Fife.
On this day, the British mini-submarine XE-4 and its five-man crew cut the undersea communications cables connecting Singapore to Saigon, and Saigon to Hong Kong. This forced the Japanese to communicate via radio, which was easier for the Allies to intercept.