Henry Southwell was born on 8 April 1895, the son the Right Reverend and Venerable Henry Kemble Southwell, Bishop of Lewes and Mrs H K Southwell of the Residentiary, Chichester, West Sussex. He joined the Royal Navy as a Cadet on 15 January 1908. He was promoted to Midshipman and, appointed on 15 January 1913 to the battleship HMS TEMERAIRE. On 28 July 1915 he was appointed to the gunboat HMS BRAMBLE deployed to the Persian Gulf.

He was promoted Lieutenant on 15 May 1917 and on 7 January 1918 appointed to HMS DOLPHIN for Submarine Training, then further appointed to HMS G11 on 30 March 1918.

On 15 October 1918 he was appointed to HMS L55 as First Lieutenant. During the Russian Intervention in 1919, L55 was sent into the Baltic. L55 was sunk with the loss of all hands after coming under fire from the Russian destroyers GAVRIL and AZARD on 4 June 1919.

The bodies of the crew of HMS L55 were recovered and returned to UK after the Russians raised the wreck of the submarine in 1928. Twenty-four-year-old Henry Southwell was a native of Chelton, Shropshire. He was buried in the Haslar Naval Cemetery in the HMS L55 Grave on 7 September 1928. The funeral service was conducted by his father, Bishop Southwell, Bishop of Lewes.