Fieldhouse became Commander-in-Chief Fleet and NATO Commander-in-Chief, Channel and Commander-in-Chief Eastern Atlantic in April 1981, and received promotion to full admiral on 23 July. Following the invasion of the Falkland Islands by Argentine forces in April 1982, Fieldhouse was appointed Commander of the Task Force (designated Task Force 317) given responsibility for "Operation Corporate", the mission to recover the Falkland Islands. He conducted the campaign, which ended in the surrender of Argentine forces in June 1982, from the Northwood Command Centre. He was advanced to Knight Grand Cross of the Order of the Bath in the 1982 Birthday Honours and appointed a Knight Grand Cross of the Order of the British Empire on 11 October 1982 "in recognition of service within the operations in the South Atlantic".