Intelligence Division, Navel Staff, Admiralty, S.W.l. 15th August, 1939 Dear Barnard, Despatch of Secret Documents by Air The Admiralty agree that documents of the highest secrecy (category(i)) should not be sent by air. 2. The Admiralty, however, consider that it is impossible to classify documents into categories (i) and (ii) in such a way that the needs of all departments will be suited. 3. As the air route will not always be over British territory or over the sea, and as adequate security at stopping places has not, so far as the Admiralty is aware, yet been provided, the present general policy is not to send secret documents by air at all.