304 Lord Cranborne, U.K. Secretary of State for Dominion Affairs, to Sir Geoffrey Whiskard, U.K. High Commissioner in Australia
Circular cablegram Z47 LONDON, 16 February 1941, 5.50 p.m.
IMMEDIATE MOST SECRET
Please give the following message to the Prime Minister  for his most secret and personal information.
1. Reference my Circular telegram Z.43 of 11th February.  Review by our military advisers of strategical implications of a Japanese southward move contains the following conclusions.
2. Japanese are now engaged on move designed to increase their hold on Indo-China and to secure strategic facilities in Thailand.
The more important of these facilities may be summarized as:-
a. Kamranh Bay which is only first-class anchorage in South China Sea, excluding British and United States possessions, and would be available as advance base for a sea-borne attack on Malaya or on British North Borneo.
b. South Indo-China where ample aerodrome accommodation is available from which Japanese might bring a light scale air attack on Malaya including Singapore.
c. Establishment of air bases in North West Thailand and Bangkok area from which a considerable scale air attack could be delivered on Rangoon and Tenasserim.
d. Control of Thai Isthmus would enable Japan to 1. attack with aircraft Singapore, Malacca Straits and Penang.
2. establish a base for land forces with a view to land attack on Malaya.
3. gain control of ports such as Muang Trang on west coast (which could be supplied overland from eastern side of the isthmus) and 4. thus facilitate operation of raiders including heavy ships against our sea communications in the Indian Ocean and particularly northern entrance to Malacca Straits.
3. Japanese may however be contemplating more drastic action which might include attack on Netherlands East Indies. The threat to our vital interests that such a move would entail does not require emphasis. The degree of such threat would depend on whether outlying islands were seized or whether attack were to include Borneo, Java or even Sumatra. In addition Japanese would probably obtain material economic gains particularly as regards oil, rubber and tropical products, these sources of supply being lost to us.
4. In these circumstances therefore in addition to immediate despatch of an Australian brigade group to Malaya other immediate steps are being taken to accelerate the reinforcement programme.
Of this programme the following are the main items:-
a. immediate despatch from India of one bomber and one fighter squadron.
b. the despatch from India of one division already earmarked is being considerably accelerated. One brigade is to leave very shortly, the second and bulk of divisional troops to arrive in Malaya in April and third brigade as soon as possible thereafter.
c. four Indian States battalions are being sent to Malaya as aerodrome guards and for internal security duties.
In addition, in view of possible threat to Burma, one infantry brigade and two batteries are being despatched from India to Burma within a month.