were originally commissioned in the British Army, with four coming from the infantry, two from the artillery and one each from the cavalry and the engineers. Of these both Lord Trenchard and Sir John Salmond each held the post over two separate periods. By the early mid-1950s sufficient time had elapsed for officers originally commissioned in the British air services of the First World War to have risen through the ranks to RAF's senior post; Sir John Slessor had originally served in the Royal Flying Corps while Sir William Dickson was commissioned into the Royal Naval Air Service. In 1956 Sir Dermot Boyle became the first CAS to have originally been commissioned in the RAF. Appointees The following list gives details of the chiefs of the air staff from 1918 to the present: The ranks and titles shown are the highest that the officer in question attained during his tour as Chief of the Air Staff. However, in the case where the officer was promoted on the day before he was posted or retired, then the lower rank is shown. See also Other service chiefs Chief of the Defence Staff (United Kingdom) First Sea Lord / Chief of the Naval Staff Chief of the General Staff (United Kingdom) Chief of Air Force (Australia) (Between 1922 and 1997, the RAAF's senior officer was known as "Chief of the Air Staff".) Chief of the Air Staff (disambiguation) Generally relevant CAS Air Power Workshop References * United Kingdom