HMS L9 was a British L class submarine built by William Denny and Brothers, Dumbarton. She was laid down on in October 1916 and was commissioned on 27 May 1918. HMS L9 was sunk during a typhoon in Hong Kong harbour on 18 August 1923. She was salved on 6 September 1923 and then recommissioned. HMS L9 was sold in Hong Kong on 30 June 1927.