When was the last VSO (US or UK) resignation on principle? - Chug
Admiral Sir David Luce comes to mind, vide the following extract from Wiki to keep it simple:
"Luce became First Sea Lord and Chief of the Naval Staff in August 1963. He resigned from the Royal Navy along with Navy Minister Christopher Mayhew on 15 March 1966 in protest over the decision by the Labour Secretary of State for Defence, Denis Healey, to cancel the CVA-01 aircraft carrier programme."
Not a resignation issue but, whilst still serving as CDS, Admiral Lord Boyce stood up pretty well to Anthony Charles Lyndon Blair regarding the legality of involvement in Iraq, as opposed to waiting until leaving office.
Jack