From 1946 to <answer>1964</answer> five Departments of State did the work of the modern Ministry of Defence: the Admiralty, the War Office, the Air Ministry, the Ministry of Aviation, and an earlier form of the Ministry of Defence. These departments merged in <answer>1964</answer>; the defence functions of the Ministry of Aviation Supply merged into the Ministry of Defence in 1971.
All former Departments of State (except the Ministry of Aviation Supply) merged in what year?
1964