My Circular M.285 of 2nd September. [1]

As you are probably aware, the Prime Minister [2] in his broadcast
on August 24th took the opportunity of making it clear to the
public that if the efforts of the United States to reach a fair
and amicable settlement with Japan should fail 'we shall, of
course, range ourselves unhesitatingly at the side of United
States'.

We have been giving further consideration to the question of
whether it would be possible to secure from the United States some
similar assurance on their part of support to us in the event of
war arising between us and Japan, as a result of some action which
we found it necessary to take in order to counter a further
Japanese encroachment in the Far East.

It will be recalled (my Circular M-203, August 2nd [3]) that the
observations of His Majesty's Ambassador at Washington were
invited as [to] the likelihood of the United States Government
being prepared to give an assurance on the above lines. In my
Circular M.213, of August 5th [4], it was mentioned that in the
view of His Majesty's Ambassador there was no reason to fear that
the President and his advisers were not fully alive to the
realities of the dangers to the British Empire in the Far East. It
was necessary, however, to appreciate the reality of
constitutional difficulties of the United States Government; if
the President were to give us an assurance of support he might, in
fact, be unable to implement it owing to Congressional opposition
or obstruction. None the less, Lord Halifax considered that if we
became involved in hostilities as a result of Japanese aggression
there would, in all probability, be very great popular support in
the United States for active intervention.

The matter was also discussed privately with the United States
Ambassador in London [5] who suggested that the particular
question of an assurance by the United States was one which had
better be taken up directly with the President by the Prime
Minister. At his meeting with President Roosevelt accordingly, the
Prime Minister sounded the President as to the possibility of an
intimation from him that, if any third power became the object of
aggression by Japanese in consequence of counter measures which it
had taken or supported to meet encroachment by Japan in the South
West Pacific, he would have the intention to seek authority from
Congress to give aid to such a power. President Roosevelt replied,
however, without hesitation, that it was constitutionally
impossible for him to go even as far as this.

In these circumstances, we feel that the matter must be left as it
stands, at any rate for the present, and so far as any question of
a formal assurance by the United States is concerned. You should,
however, be aware that the general impression derived by our
representatives at the Atlantic meeting was that, although the
United States could not make any satisfactory declaration on the
point, there was no doubt that in practice we could count on
United States' support if, as a result of Japanese aggression, we
became involved in war with Japan. In this connection, I should
also invite attention to my Circular M.2[3]8 [6] of August 12th
[7], which indicated that the United States' Ambassador at Tokyo
[8] had made it clear to the former Japanese Minister for Foreign
Affairs [9] that as the United States are doing everything in
their power generally to keep us supplied across the Atlantic,
they obviously could not stand by and watch our lifeline being cut
in the Pacific through an attack on Singapore or the Netherland
East Indies.

The President assured His Majesty's Ambassador at Washington on
July 31st that this would still be the United States' attitude in
the event of such a Japanese attack and, as mentioned in my above
telegram, Lord Halifax was later informed by the United States'
Secretary of State [10] that this general definition of the United
States' position had recently been conveyed by Welles [11] and
himself to the Japanese Ambassador and Counsellor at Washington.

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