Air Marshal Sir Leonard Horatio Slatter, KBE, CB, DSC & Bar, DFC, DL (8 December 1894 – 14 April 1961) was a naval aviator during the First World War and a senior Royal Air Force commander during the Second World War. Slatter ended his career as the Air Officer Commanding-in-Chief of Coastal Command.
Slatter was born in Durban, South Africa on 8 December 1894. He received his education at Dale College and Selborne College in South Africa and then at Battersea Polytechnic, training to be a civil engineer.
With the outbreak of the First World War he joined the Royal Navy. He initially served as a dispatch rider in the Naval Armoured Car Division before transferring to the Royal Naval Air Service in 1915. After successfully completing his observer training, Slatter was posted in February 1916 to the Seaplane Squadron at Dunkirk.
In July 1916 Slatter started his training to be a naval pilot and later in that year he commenced flying duties at Royal Naval Air Station Dover. February 1917 saw Slatter posted to the Seaplane Defence Flight (later to become No. 13 (Naval) Squadron and then No. 213 Squadron RAF) as a pilot operating out of Dunkirk. During this time Slatter shot down six enemy aircraft, and was advanced from pilot to flight commander.