39 Mr R. G. Menzies, Prime Minister, to Lord Cranborne, U.K. Secretary of State for Dominion Affairs
Cablegram 523  CANBERRA, 11 August 1941
MOST IMMEDIATE MOST SECRET
Following for the Prime Minister  from the Prime Minister.
My colleagues and I have given anxious consideration to the Far Eastern position.  We have, as you know, always regarded Singapore and Malaya as our vital outpost, and have at all times, as I indicated to the Foreign Office when in London, been prepared to join in a guarantee to the Netherlands East Indies. 
We have also assumed that in the event of war with Japan naval reinforcements as discussed in London, with a nucleus of five capital ships, would be sent to the Far East. We now say and emphasise that an early despatch of capital ships east of Suez would itself be the most powerful deterrent and first step.
We also once more urge that, having regard to the grave tension at present existing, air and military reinforcements to Malaya should be vigorously expedited.
The position of Thailand now comes up for early decision for events appear to be moving rapidly. Two urgent questions emerge:-
(1) Should we, the British countries, be prepared to make it clear to Thailand and to Japan that any attack upon Thailand by Japan will be regarded by us as a casus belli;
(2) Should we announce this to the countries concerned independently of United States action, or should we make it conditional upon American concurrence and active participation.
We are of opinion, as the Government of one of the two British Dominions which are most directly affected, that the first question should be answered 'yes' and that while every pressure should be maintained upon the United States, it would be an error to condition our action upon American action, though actual objection by the United States of America would of course be fatal.
Thailand's strategic position and resources are such that Japan's occupation of them would gravely imperil the safety of Singapore, the effective control of the waters around the Malay Peninsula, the Philippines and the Netherlands East Indies, and the maintenance of Chinese supplies along the Burma Road.
Having regard to the realities in the Far East, we do not believe that Japan wants Thailand merely as an end in itself. Its capture or control would be plainly a first step, and it is the first step that counts. In this connection we have noted with regret that Mr.
Sumner Welles' warning to Japan seemed to indicate that the objectionable matter would not be the occupation of Thailand but only what might happen subsequently. 
The attitude of the United States, while constitutionally and politically understandable, is disappointing. We have throughout this period felt that a clear and unequivocal statement to Japan by the United States would have stopped aggression. Up to the time of the coup in Indo China it had not been made. Later on, Sumner Welles made a much more vigorous statement to a Japanese representative, though it is subject to the criticism mentioned above. But the Japanese have still not been given a firm warning.
Indications of postponed resistance to aggression are a mere encouragement.
We feel that if we are prepared to fight America will not in fact desert us. A bold course might change the whole outlook.
Naturally, in all this we are assuming that whatever we do will be done in the closest consultation and agreement with the Netherlands East Indies.
Subject to above, our view can be summed up as being that if Thailand is abandoned and we delay our action we will be one country nearer to war and that in that war and in particular in the defence of Singapore, Japan will be relatively stronger and we relatively weaker than at present.
We express these views frankly and with realisation of their implications so that you may see the supreme importance which we attach to them.