Thomas Leonard was a member of the Mercantile Marine Reserve. He is listed without a service number.

Notice that he died in March 1919, four months after the war had ended. Without further information, the most likely reason would be influenza, which seems to be confirmed below. HMS Mantua certainly visited Barrow in 1919.

HMS Mantua was an armed Merchant Cruiser belonging to the Pacific & Orient Line, and was returned to civilian service in December 1919 (http://old.oldweather.org/vessels/4caf8827cadfd3419701eb91 ) One of 69 armed merchant cruisers commissioned in World War 1, liner, 10,885grt, built 1908, http://www.naval-history.net/OWShips-WW1-08Mantua1.htm HMS Mantua saw service in the following roles during WW1: Mar 1915-Oct 1916, Northern Patrol; Apr 1917-Jan 1919, Sierra Leone (convoys), Cape of Good Hope (convoys).

In The Great Influenza: the story of the greatest pandemic in history, (2005) John Barry says ‘On August 15 (1918) HMS Mantua called into port (Freetown, Sierra Leone) with 200 crew members suffering from influenza. He goes on to describe the effects of the spread of influenza among the crews of other ships and the local labourers, who were used for coaling the ships.

Wikipedia reports: In August 1918, a more virulent strain appeared simultaneously in Brest, Brittany-France, in Freetown, Sierra Leone, and in the U.S. in Boston, Massachusetts. The Allies of World War I came to call it the Spanish flu, primarily because the pandemic received greater press attention after it moved from France to Spain in November 1918. Spain was not involved in the war and had not imposed wartime censorship. http://en.wikipedia.org/wiki/1918_flu_pandemic

Pictures of the Mantua can be found at http://www.simplonpc.co.uk/PO_Liners2.html#anchor7350