When Japan entered the war in December 1941 it was clear that Britain was not willing to divert extra resources to the Pacific. When two British warships, Prince of Wales and Repulse, were sunk by the Japanese off Malaya it was also clear that Britain was not able to help. The Japanese swept through Malaya, taking the supposedly impregnable port of Singapore within a few weeks. This sent shock waves through the Australian community, which was further devastated with the news that the whole of the 8th Division had surrendered to the Japanese and become prisoners of war in February 1942. Australians knew that Darwin and Broome had been bombed from February to November, but government censorship kept many of the details of the extent of the damage from the public. The censorship was meant to prevent any panic in the southern States about an imminent Japanese invasion, but most Australians were aware of the danger. They were certainly left in no doubt of their vulnerability in May and June 1942 when Japanese submarines shelled the coastal suburbs of Sydney and Newcastle, and launched midget submarines into Sydney Harbour, one of which sank a ferry, killing 19 sailors.
Curtin's famous declaration that 'Australia looks to America, free of any pangs as to our traditional links or kinship with the United Kingdom' was the only realistic option since Australia was not capable of defending itself without help against a Japanese invasion. For the USA, Australia was a valuable base from which to halt the Japanese advance and then to push it back. Curtin welcomed General Douglas MacArthur as head of the American forces, and for the first year or two got on well with him, despite the obvious loss of Australian sovereignty that the American presence involved. He did not get on nearly as well with Prime Minister Churchill, with whom he had regular and heated arguments by cable about the deployment of Australian troops. The interests of Australia were not the prime concern of either Britain or the United States, so that Curtin's attempts to assert those interests or to participate in decisions about the conduct of the war were not well received in London or Washington. After the war these relationships set the stage for the cementing of the ANZUS treaty that has become one of the pillars of Australian foreign policy since that time.
Curtin's contribution was to fully mobilise Australian society to endure the hardships of war. Rationing was introduced and price controls enforced, although a black market flourished. A decision of the High Court in 1942 validated the Commonwealth's takeover of income tax from the States. Industry was effectively focused on the war effort both by the imposition of controls and the appointment of talented businessmen such as Essington Lewis to key posts, as also by the direction of man and woman-power to strategic industries. The Labor government was successful in persuading Australians that these difficult decisions were necessary.
Probably the most painful decision for Curtin was his recommendation to the Federal Conference in November 1942 that militia units be made available for deployment in the Pacific theatre outside Australia's borders. For most of the labour movement this was a revival of the debate about conscription that was considered settled in 1916. Curtin was able to convince the party that the measure was for the purpose of the direct defence of Australia (which party policy had traditionally supported), but it resulted in fierce criticism of the Prime Minister not only from the union movement, but also within the Caucus. Curtin always had to contend with opposition from strong-minded individuals in his Cabinet and Caucus, but one of the measures of his success as Prime Minister was his effective resistance to the criticisms of heavyweights like Herb Evatt, John Beasley, Eddie Ward and Arthur Calwell. On the other hand he always had the support and comradeship of his Treasurer, Ben Chifley.