There have been, to date;
Six former 1st Sea Lords; Mountbatten, Hill-Norton, Ashmore, Lewin, Fieldhouse and Boyce who have held the office of CDS.
Seven former CGS'; Hull, Carver, Brammall, Inge, Guthrie, Walker and Richards
Seven former CAS'; Dickson, Elworthy, Humphrey, Cameron, Craig, Harding and Stirrup.
There have been three former VCDS' who have been appointed directly to the post; Vincent and Houghton (Army) and Peach (RAF).
Most of the Army appointments appear to be post MRAF Harding's resignation in 1994. Sir William Dickson was the first wholly appointed head of HM Forces overall in 1956, when the title was still the dual hatted 'Chairman of the Chiefs of Staffs Committee. He was still incumbent when the title changed to Chief of the Defence Staff on 1 January 1959 relinquishing the appointment in July that year. Dickson was chosen, so it is said, to be the first full time HM Forces chief due to the prominence of the RAF in the 1950s, with the height of the Cold War and the reliance on the nuclear strike capability which at the time was essentially delivered by the then growing V-Force. The shift to a more Land warfare background came into vogue with the post-cold war expeditionary nature of conflicts in the Balkans, Iraq, Afghanistan etc.
Here endeth the Sermon!
FB