Air Marshal Sir Leonard Horatio Slatter KBE CB DSC with bar DFC RAF (8 December 1894 – 14 April 1961) was a naval aviator during World War I and a senior Royal Air Force commander during World War II. Slatter ended his career as the commander-in-chief of Coastal Command.
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 five enemy aircraft and was advanced from pilot to flight commander.
In July 1918, Slatter was removed from front-line duties and sent to No. 4 Aeroplane Supply Depot as an instructor. Even though he was officially excluded from operations, Slatter succeeded in flying over the front and shot down his sixth and final enemy aircraft on 30 August 1918.
After his return to Great Britain, Slatter took up duties as a flight commander on No. 205 Squadron at RAF Leuchars. In 1921, Slatter was posted to No. 203 Squadron, still based at Leuchars, flying Nightjars. He later became the squadron's commander whilst the squadron was deployed in Turkey. 1922 saw Slatter transferred again, this time to No. 230 Squadron where he served as both a flight commander and as the officer commanding. In early 1924 Slatter was substantively promoted to squadron leader and posted to Malta where he served as the commander of the RAF base for over two years. On his return in 1926, Slatter spent a few months as a supernumerary at the RAF Depot.
In late 1926, Slatter was appointed Officer Commanding the RAF High Speed Flight at the Marine Aircraft Experimental Establishment. Slatter was responsible for preparing his team to compete in the 1927 Schneider Trophy competition in Venice. Slatter himself flew the Crusader but crashed before competing and Slatter suffered only bruising and facial injuries.