152 Mr R. G. Casey, Minister to the United States, to Department of External Affairs
Cablegram 1064 WASHINGTON, 1 December 1941, 11.48 p.m.
British Ambassador  saw the President  today. Following is British Ambassador's telegram to London practically textually.
(1) President's information was that Japanese Government was a good deal disturbed by his return. He told me that the Japanese had returned to the subject of the interim arrangement, and Hull  had replied to the effect that the interim arrangement was not possible on a unilateral basis which was the basis on which Japanese were proceeding inasmuch as they were continuing moving troops all the time.
(2) President told me that he thought we should both continue our air patrol for further period which he did not specify. He had also given orders for three United States submarines to watch likely waters for sake of information. They would not take offensive action but would act if attacked.
(3) He then discussed Japanese reinforcement of Indo-China and said he had been considering the possibility of some concerted action parallel with us. He thought, however, that wiser course was to begin by making communication to Japanese in form of a question which he proposed to instruct Sumner Welles to give to Japanese this evening or tomorrow morning on lines enquiring where Japanese troops now moving south were going to, and if they were going to Indo-China, for what purpose. 
(4) I asked what would be next step since Japanese reply would certainly be either puzzling or evasive seeing that there could be no possible legitimate reason for such reinforcement of Japanese strength in Indo-China.
(5) President said he thought it was of great importance that British and American Governments should be clear in their minds as to what they did in various hypothetical situations that were likely to arise.
(6) He wished me to ask you what the British Government would do in the event of (a) Japanese reply being unsatisfactory, further reinforcements not yet having reached Indo-China; (b) reply being unsatisfactory further reinforcements having in the meantime reached Indo-China; and (c) Japanese attack on Thailand other than attack on Kra Isthmus, having in his mind such Japanese pressure on Thailand as to force concessions to Japanese detrimental to general position.
(7) Grateful for prompt replies to above. I think whatever action you are prepared to take, President would probably support. Method of support is presumably for staffs but he spoke all the time of United States air strength in Philippines and long distance naval blockade 'which of course means shooting'.
Whole tenor of his conversation, though he did not actually say so, was in sense that we should both recognise any of these hypothetical actions to be clear prelude to some further action and threat to our common interests against which we ought to react together at once.
At one point he threw in an aside that in the case of any direct attack on ourselves or the Dutch we should obviously all be together, but he wished to clear up matters that were less plain.
(8) In reply to my query as to the British forestalling the Japanese in the Kra Isthmus, and as to what would be American reaction to such an action on our part, the President said that we could certainly count on their support  though it might take a short time, he spoke of a few days, to get things into political shape here.
In this connection he told me that they had information that someone in the Japanese Embassy, Bangkok, had advised Tokyo to make the first attack on British territory just south of the Malay-Thai boundary, the argument being that this would immediately oblige us to occupy position on the isthmus in Thai territory and give Japan the advantage of making us the first to commit an aggression against the Thais.
He said that if we could get the Thais to invite us it would obviously be a good standby, but we must clearly do what strategic necessity dictated anyhow.
(9) From various indications, including information that discussions are proceeding between the Japanese and Germans about the distribution of rubber from Indo-China, he has little doubt that there is complete understanding between Berlin and Tokyo and that the Japanese are playing a game stalling for time while proceeding with their own policy at the dictation of the Axis. He was quite clear that there was nothing to be made of any idea of a standfast truce.
(10) He has an idea of sending a communication direct to the Emperor which he said had been the only thing that had worked at the time of the 'Panay' incident.  Such a communication would be friendly but would make plain that if the present Japanese policy continued war must result.
He is, however, suspending this for the present.
(11) He wished me to convey the suggestion that we should give the Thais an undertaking if they resisted either Japanese attack or infiltration that we would respect and guarantee for the future their full sovereignty and independence. For constitutional reasons the United States could not guarantee, but such an undertaking on our part would be wholeheartedly supported by the United States. Presumed the Dutch would also agree.
He thought that this might be very valuable against Japanese propaganda or intimidation.