Leonard was born in Hackney, London on 14 February 1925 to Latvian-born father David and London born mother Elizabeth nee Solomons and was the youngest of four children. Leonard wanted to be a pastry chef and was upset when his father insisted that he joined the family coat manufacturers business, so at the age of seventeen he ran away and joined the Navy lying about his age.

After training he was transferred to the light cruiser H.M.S. Birmingham as an ordinary signalman for lamps and flags. In November 1943 the ship was in convoy travelling from Scapa Flow to Alexandria in Egypt. On the night of the 28 November the ship was torpedoed by U-boat U-407 off the coast of Cyrenaica. The damage was mostly to the signalman’s mess and twenty-seven men were killed. After the ship was escorted to Alexandria for repairs, Leonard was buried in Alexandria (Hadra) War Memorial Cemetery and a token in his memory was placed on his parent’s grave.