(Due to arrive Melbourne 14.3.25)
My dear P.M.,
SECRECY OF CERTAIN DOCUMENTS
It has been pointed out to me that, whilst the secrecy of the majority of documents depends on their freshness and evaporates with time, there are others which are from their nature never to be divulged. In the latter category comes such a document as W.7., which I send in this envelope, a comprehensive summary of what measures the C.I.D. are taking to prepare for another war.
I was told the fact that quite a considerable personal correspondence goes on continually between the Secretary of State for India and the Viceroy. This correspondence is private and the papers are the personal property of the Viceroy and, at his discretion, are taken away or destroyed by him, on his successor taking office.
Papers of importance sent out to you by me could, of course, at your discretion, be so treated. 
I am, Yours very truly, R. G. CASEY