26 Mr R. G. Menzies, Prime Minister, to Lord Cranborne, U.K. Secretary of State for Dominion Affairs
Cablegram 499  CANBERRA, [2 August 1941] 
My telegram 486 of 30th July : we assume that the approach to the United States Government will be comprehensive and will attempt to elucidate United States attitude not only in general contingency of war in the Pacific arising out of retaliatory measures taken against Japan but also in relation to specific questions of Netherlands East Indies and Thailand. We are strongly of opinion that the piecemeal consideration of possible developments in East Asia and the Pacific is no longer satisfactory and that effort should now be made to define a, line which the British Commonwealth and the United States of America might follow in this region in conjunction.
1. N.E.I. Since receiving your telegram 440 of 21st June  we are not aware that any further consideration has been given to the question of (a) declaration, or (b) a private assurance of support to the Netherlands East Indies in the event of an attack by Japan on Dutch territory. We understand, however, that the British Ambassador in Tokyo  privately conveyed to the Japanese Minister for Foreign Affairs' in effect that forcible Japanese action against the Netherlands East Indies would involve the British Empire as an ally of Holland.  Presumably the corresponding assurance has not yet been given to the Netherlands Government although it is noted from your telegram M. 167  that consultation took place with the Netherlands Government regarding Dutch co-operation in present economic restrictions against Japan.
The Commonwealth Government would be glad to know what your present views are on this matter. We are inclined to doubt whether any good purpose will now be served by attempting to renew the proposals from the point where they were left in June, i.e., on the basis of a unilateral public declaration or private assurance by the British Empire, leaving the question of United States participation to be settled subsequently. In the circumstances that have arisen since that date, it seems to us desirable that consideration of the matter should now be on the basis of an understanding or assurance on the part of the United States. 
If this is accepted, we assume that maximum use will be made with the United States Government of the important argument that both Netherlands East Indies and Malaya are major sources of supply to the United States for essential war materials, notably rubber, which it would be greatly to the advantage of the Axis to cut off.
2. THAILAND. On indications that Japan is contemplating some early move towards subjection of Thailand, we consider that this contingency should also be urgently raised with the United States Government. We are strongly impressed with the views of the British Minister at Bangkok , and Sir John Latham  has also expressed from Tokyo his opinion that we should, without delay, enlist the co-operation and support of the United States in handling the matter. We entirely endorse this view and suggest that as preliminary step the British Ambassador in Washington  should be asked to ascertain, in conjunction with his general approach to the United States Government, what course of action the United States Administration has in mind, either as a deterrent to Japan or as a counter measure in the event of fulfilment of Japanese designs.