19 Lord Cranborne, U.K. Secretary of State for Dominion Affairs, to Commonwealth Government
Cablegram 515 LONDON, 26 July 1941, 9.07 p.m.
MOST IMMEDIATE MOST SECRET
Japan: Your telegram 25th July, 477. 
1. We are very glad to know that the Commonwealth Government agree with our view both as to the difficulty in the present circumstances of securing a guarantee of armed support from the United States and also as to the inadvisability of our informing the United States that in taking our action we have done so on the assumption that we can rely on their armed support if need arises.
2. In our judgment it would have created deplorable effect on the United States Government if the latter had gained the impression that we were seeking to attach conditions to our action or were not wholehearted in following their lead. We are convinced that the right course was to act quickly and without reservation.
Indeed, the importance in relation to public opinion both in Japan and the United States of our appearing closely united with the United States Government on this issue can in our view hardly be over-estimated.
3. A further point of material significance was that although the United States Government at first hinted that they did not necessarily expect our action to be taken simultaneously with theirs, they later let it be known to His Majesty's Ambassador  that they had delayed their action until today in order to give us time to reach a decision ourselves.
4. Nevertheless we would assure you that we entirely appreciate and indeed share the preoccupations expressed in your telegram.
The objective which we both have in view is to secure from the United States Government the clearest possible indication of their support, and if we are counselling a less direct method of approach on this question it is merely because we feel sure that this will in fact prove to be the best means of securing the desired result. In defining our attitude in paragraph 4 (3) of my Circular M.172 , we said that 'if we are called upon to go to lengths which involve the plain risk of war with Japan every effort should be made etc.' Whether the action now taken by the United States and ourselves will involve the plain risk of war depends in the first instance on the reactions of Japan and these cannot yet be estimated. The object both of the United States measures and our own is to deter Japan and if possible deflect her from the course which less strong counter measures might encourage her to pursue.
5. We agree, however, we must in any case expect a state of tension for some time ahead, the outcome of which must hang in the balance and now that we have boldly followed the United States lead and taken parallel action with them without reservations, we should see less objection to opening the question of an assurance with the United States Government at the earliest suitable opportunity. In our view the appropriate line of approach would be to say to them that measures corresponding to theirs having been taken both by ourselves and by the other British Commonwealth Governments, we sincerely hope that our united action will succeed in achieving the object of deterring Japan from her programme of southward expansion. We must naturally be prepared, however, for the possibility that the measures taken may have the contrary effect of driving Japan to some further move. We are, of course, fully alive to this risk and are doing what we can in our own defence. But naturally what would have the greatest deterrent effect and a correspondingly encouraging effect on those more directly threatened by her present move would be the clearest indication that the United States Government feel able to give assurance that we can count on their support if we are attacked by Japan or become involved in war with her through an attack on the Netherlands East Indies.
6. On the assumption that this would meet the views of the Commonwealth Government we will consult His Majesty's Ambassador as to the most suitable moment for the approach on these lines.