Read this and answer the question. If the question is unanswerable, say "unanswerable".

From 1946 to 1964 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 1964; the defence functions of the Ministry of Aviation Supply merged into the Ministry of Defence in 1971.

What happened to the War Office in 1971?
unanswerable