372 Mr R.G. Casey, Minister for Supply and Development, to Mr R.G. Menzies, Prime Minister

Cablegram C26 LONDON, 17 November 1939

MOST SECRET FOR PRIME MINISTER

Precis of naval appreciation of Australian naval defence. Begins.

(1) A Japanese attack upon Singapore would require at least fifty thousand troops to undertake siege operations for some four or five months in difficult country with all the disadvantages of a long line of communications liable to interruption at any time if Great Britain chose to send superior force. It is not considered likely that Japan would embark upon such an enterprise.

Invasion of Australia is regarded as even less likely as this would involve the despatch and maintenance of a large army with a much longer line of communications, liable to be cut at any time by a British fleet arriving in the area.

Apart from the fact that such an operation would be resented by the United States, as long as there is a well-armed Australian military force and a superior British fleet in being in any part of the world it is needless to suppose such an enterprise would be attempted.

(2) Long range action by submarine or raiding cruiser is always possible but beyond temporary inconvenience by disturbing coastal trade unlikely to cause much damage.

(3) Power of predominant fleet is exercised simultaneously in all quarters of the globe in which it has bases irrespective of the station it occupies at any given moment provided it is not permanently tied to that station.

Naval situation at present quite different to that pertaining during the last war. Admiralty contemplated fighting Italy in the Mediterranean and German U-boats in the North Sea and Atlantic with the aid of the French fleet which is very efficient and strong as Italian and that Italy would have been defeated within a few months.

Even if the result in Mediterranean had been long delayed, the Admiralty were prepared to dose the Mediterranean at Gibraltar and Suez Canal and sacrificing important interests in that area proceeding to relief of Singapore or aid of Australia in the event of serious attack.

With Italy neutral British fleet is again entirely mobile and although not at present able to place superior battlefleet in Japanese home waters it is possible if necessary to place a squadron battleships at Singapore or Australian waters sufficient to act as major deterrent on Japanese action so far from home.

This would of course be done from the moment that danger to either Singapore or Australia developed in a manner which made their protection a real and practical war need.

The Admiralty accept full responsibility of defending Australia or Singapore from a Japanese attack on a large scale and have forces at their disposal for these essential purposes.

The Admiralty most grateful to War Department for loyal and clairvoyant strategy which has to the uninstructed eye denuded Australia of naval forces. Assistance of Australian destroyers is invaluable. The Admiralty regard the defence of Australia and of Singapore as a steppingstone to Australia as ranking next to the mastering of the principal fleet to which we are opposed and the duty of defending Australia against serious attack would take precedence over British interests in the Mediterranean. It is very unlikely bleak choice will arise during next year or two.

Our naval strength is steadily improving as new battleships come into service and there are no naval grounds for assuming (action) which should prevent the despatch of Australian Army to decisive battlefield where their name stands so high. Ends.

Am having a conference on the Far East statement and on above statement on Monday afternoon and will cable you the result.

CASEY

[AA: A1608, A41/1/1 vi]