Before the war, Australians felt that they were a part of the British Empire. When war broke out in September, 1939, the Prime Minister of Australia (Menzies) sent their best troops to the Middle East and North Africa, to help the British. There were two types of armies in Australia. The AIF, well trained men, and the other army, back in Australia, was a badly trained, low morale 'men', which were made into a small force called the militia. Most of them were under 21 years of age, they were town boys from suburbs from Melbourne and Sydney. They were called 'Chocolate Soldiers' the term 'Chocolate Soldiers' was coined by the AIF because they were poorly trained and they thought they would melt in the heat of battle. The war got so serious that the 39th Battalion was formed, and they took everyone who enlisted.
On the 7th of December 1941, the American naval base at Pearl Harbour was bombed by the Japanese, entering the United States of America into the war. One day after Peral Harbor John Curtin, Menzies replacement delivered a message to the nation of Australia, that we were at war with the Japanese, because the Japanese were so close to Australia, and saw the destruction that the Japanese could unlesh at Pearl Harbour. Australians had to fight for Australia.
While still training on Victoria, the 39th Militia were called into service, to guard the tropics of Papua New Guinea, but men like the ones in the 39th Militia, they were not allowed to serve overseas, but there was a loophole, Papua New Guinea was an Australian Mandated Territory.
The Militia were based in Port Moresby, to defend it from the Japanese. the 39th linked up with the 53rd Militia, also poorly trained. When they got to New Guinea, there orders were to garrason Port Moresby, build an airfield and defend it (Airfields ment much to the Pacific War because it was about who controlled the air).
Meanwhile, the Japanese swiftly took Indochina, Malaya and Thailand. On the 23rd of January 1942, 5000 Japanese Soldiers captured Rabaul - the Capital of New England, just of the coast of Papua New Guinea. On the 15th of February 1942, Japan attacks Sinapore and takes just under 15,000 Australian Prisoners, when Britain surrendered Singapore, on the 19th of February 1942, Japanese aircraft bombed Darwin, killing over 250 people and also destroying the port and 9 ships and 20 aircraft. This put Japan into a position that could invade Australia; and many people belived so.
On the 11th of March, 1942, the Japanese surrounded 70,000 American and Filipeno troops in the Philippiens, President Roosevelt ordered the commander General Douglas MacArther, to take control of Australia and contol the war in the South West Pacific. he was given full control of Australian forces.Having the Rabaul airfiled the Japanese were able to keep there rapid advance towards Australia, they bombed Port Moresby with a series of Bombing raids. The only defence of Australia were the 39th and 53rd Militia and few US troops, Curtain now realised that the Militia could not hold the defence of Port Moresby, he took a stand against the mother country, he ordered 20,000 AIF troops from the Middle East and North Africa to return from Australia. The AIF arrived at Australia in early March 1942, but they didn't go to Port Moresby to help the Militia; they went to Queensland because intelligence suggested there was a greater chance of invasion there.
While the AIF made a line of defence outside Brisbane, the Japanese aircraft carriers and troopships tried to invade and occupy Port Moresby by sea, a group of US and Australian pilots fought them on the 4th of May 1942, at the Battle of The Coral Sea, the Allies succeeded, the Japanese could not take Port Moresby.
The Japanese Navy asked the Army to take Port Moresby by an overhead route, however, the Navy gave wrong intelligence, the Navy said there will be a road which would lead you to Port Moresby, but the road was a steep mountain track, which was long and high. The Japanese would climb over the Owen Stanly Range. MacArthur was informed of this but ignored it, he belived that climbing the Owen Stanley Range was impossible to cross, and it was NOT the Japanese plan. MacArthur had other plans, he sent the 39th Militia to occupy Kokoda and it's airfield. Kokoda was at the foothills of the Owen Stanly Mountains. Going to Kokoda was not was not easy as it sounded, the 39th went to Kokoda in wet terrain, and harsh weather.