139 Lord Cranborne, U.K. Secretary of State for Dominion Affairs, to Mr John Curtin, Prime Minister
Circular cablegram M406 LONDON, 30 November 1941, 2.40 a.m.
MOST SECRET AND PERSONAL MOST IMMEDIATE
Following for the Prime Minister.
My telegram M.405. 
1. There are important indications that Japan is about to attack
Thailand, and that this attack will include a Seaborne expedition
to seize strategic points in the Kra Isthmus.
2. The Royal Air Force are reconnoitring on an arc 180 miles from
Khota [Bharu]  for 3 days commencing 29th November and the
Commander in Chief Far East  has requested the Commander in
Chief of the United States Asiatic Fleet at Manila  to
undertake Air reconnaissance on the line Manila-Camranh Bay on the
same days. The Commander in Chief in the Far East has asked for
permission to move into the Kra Isthmus if reconnaissance
establishes the fact that escorted Japanese ships are approaching
the Isthmus, and he is pressing for an immediate decision on this
point. Time is the essence of this plan particularly at this
season of the year when the Kra Isthmus is waterlogged.
Consequently great tactical advantage lies with the side which
gets there first.
3. Our military advisers fear that operations might lead to a
clash which might involve us in war, and they have always
emphasized that unless our vital interests were immediately
threatened, this should be avoided so long as we have no certainty
of United States' support. In view however of the United States
Government's constitutional difficulties, any prior guarantee of
such support is most unlikely.
4. In these circumstances, His Majesty's Ambassador at Washington
 has been instructed to explain the position at once to the
United States Government and to take the following line. To allow
the Japanese to establish themselves so near the Malay frontier
would be an obvious threat to Singapore even though at the present
season it might not develop at once. We have also to bear in mind
the encouragement which the Japanese success would give their
extremists. The Japanese appetite would inevitably grow and other
Far Eastern peoples would [be] correspondingly depressed. It
looks, therefore, as though to ensure the defence of Singapore and
for wider reasons we might have to take the proposed action to
forestall the Japanese.
5. Lord Halifax is to ask for an urgent expression of the United
States Government's views and has been reminded of the importance
of ensuring ourselves of United States support in the event of
6. We should be grateful of your views by most immediate telegram.
[AA : A1608, A41/1/5, iv]