Air vice-marshal Sir Francis John Williamson Mellersh, KBE, AFC (22 September 1898 – 25 May 1955) was a Royal Naval Air Service aviator and flying ace credited with five aerial victories during the First World War, and a senior commander in the Royal Air Force during the 1940s and 1950s.

Mellersh joined the Royal Naval Air Service in 1916.

He trained as a fighter pilot and was posted to 9 Naval Squadron in 1917.

While flying a Sopwith Triplane on 28 July 1917, he drove down an Aviatik C. He switched to flying a Sopwith Camel and scored victories 15 October 1917 and 12 April 1918; the latter win was shared with squadron-mate Roy Brown.

On 21 April 1918, Mellersh was a flight commander involved in the dogfight that brought down the Red Baron, Manfred von Richthofen; Mellersh claimed a Fokker Dr.I triplane destroyed on that date.