Leonard was born on 20 February 1917 in Hull, Yorkshire to Simon and Jeanette nee Pineles who were also born in Hull. Leonard had two older sisters Rosalie and Adele and their father was a furniture dealer and an antiquarian. By 1939, the family were living in Brighton, East Sussex and Jeanette had remarried to Walter Benton, a publisher, and the three children had taken his surname. In 1939, Leonard was listed as working as a secretary to a building estate before he enlisted in the Navy.

In May 1941, Hood and the battleship Prince of Wales were ordered to intercept the German battleship Bismarck and the heavy cruiser Prinz Eugen which were en-route to the Atlantic, where they were to attack convoys. On 24 May 1941, early in the Battle of the Denmark Strait, the Hood was struck by several German shells, exploded, and sank within 3 minutes, with the loss of all but three of her crew of 1,418.