It was called the Australian Imperial Force as the WW1 army had been. Naturally it gathered the non official prefix of second and has been called the Second AIF ever since.

Because Battalions had a strong local support base there was huge community pressure to keep Battalion numbers the same as WW1, which led to the decision to label Battalions 'Second' so we got the Second First Battalion (2/1st Bn AIF) and the Second Twenty Ninth Battalion (2/29th) etc...

There was no such pressure to maintain divisional numbers so the divisional numbers ran on from the numbers (1 through 5 inclusive) used in WW1.  So we got the 6th, 7th, 8th and 9th Divisions AIF. 10th Division was started but never completely formed.

As well there was the CMF (Militia) Divisions and Battalions which had completely separate numbers, some of which were the same as former 1st AIF units. Many of the 1st AIF Battalion numbers were held by CMF Units. Confused? Don't worry, it all falls into place.

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The rise of Adolf Hitler in Germany, Mussolini's invasion of Abyssinia and the Spanish Civil War were signs that could not be ignored. The Munich Pact of 1938 came as a disillusioning shock and the country suddenly became aware of the pitiful inadequacy of it's defences.

Ill worked and under immense pressure, Prime Minister Lyons cracked under the strain and died in April 1939, and when war came on September 3, the main burden fell on his successor, Robert Gordon Menzies.

Recruiting for the three services began at once and the response was keen. Compulsory military service was reintroduced, with the proviso that conscripts would be required to serve only in Australia and it's territories. Naval vessels in reserve were recommissioned and work began on building others. Efforts were made to supplement from abroad Australia's 164 combat aircraft, most of which were already obsolete and Air Force volunteers were sent to Canada to take part in the Empire air training scheme.

Two AIF divisions, the 6th and 7th, were formed under Lieutenant-General Thomas Blamey and sent to Palestine for training. They were meant for service on the western front but by June 1940, France, Belgium, Holland, Denmark and Norway had been overrun and no western front remained. However their future was automatically settled when Italy came into the war on Germany's side and begun a major offensive in North Africa aimed against Egypt and the Suez Canal. The Allied counter-attack, launched in December, was spearheaded by the Australian and New Zealand troops. By late February Bardia, Tobruk, Derna and Benghazi had fallen, many thousands of prisoners had been taken and the Italians were in full retreat.

Meanwhile Australian warships had been active with the British fleet in the Mediterranean. The Sydney had sunk the Italian cruiser Bartolomeo Colleoni, and Australian ships had been conspicuous in the battles of Taranto and Matapan.

The arrival of strong German forces with powerful air support transformed the situation in North Africa, and the Allies began a fighting retreat. In March 1941 the Australian 6th Division was relieved by the newly-arrived 7th and 9th and moved to Greece, where a German invasion was imminent. It came, in overwhelming strength, during April. By the end of the month Greece had fallen and Allied troops had withdrawn to Crete. In turn Crete fell to an airborne invasion and by early June the surviving Australians were back in Egypt. With hardly time to rest or regroup they went into action in Syria and Lebanon against the Vichy French, who were beaten in a five-weeks' campaign. Meanwhile Benghazi and Derna had fallen to Rommel's Afrika Corps; Tobruk, garrisoned by the Australian 9th Division and British troops, was under siege; and Egypt was threatened.

In Australia the Menzies government had narrowly survived a general election in October 1940. The following August Menzies was supplanted by A. W. Fadden (Country Party); and two months later the government was defeated and Labour took over with John Curtin as Prime Minister.

Hitler's invasion of Russia in August 1941 radically changed the situation in Europe; and the whole pattern of the war was reshaped on 7 December when Japanese aircraft devastated a United States fleet at Pearl Harbour and massive Japanese forces invaded South-East Asia. The myth of Singapore's impregnability was shattered three days later when the British battleships Repulse and Prince of Wales were sunk off Malaya; and bitter jungle fighting followed as the Australian 8th Division and other Allied troops opposed the enemy's advance down the Malayan peninsula. Once Singapore was in Japanese hands Australia would be seriously threatened and Curtin readily agreed to Winston Churchill's suggestion that the 6th and 7th Divisions should be transferred from Africa to the Dutch East Indies. But the sheer pace of the enemy advance ruled this out. Singapore fell on 15 February 1942 and for most Australian survivors the next three and a half years meant Changi prison or slave-labour on the Burma railway.

On 19 February Japanese carrier-based bombers attacked Darwin, sank eight ships and killed 240 seamen, troops and civilians. The war was coming uncomfortably close. On 23 February, against a strong protest from Winston Churchill, Curtin ordered the returning troops to be diverted to their own country. Ten days later Japanese aircraft raided Broome, destroyed several combat aircraft and eight flying boats which were bringing civilian refugees from Java and killed about seventy people.

Australia's position was critical. Her fighting strength comprised 46,000 veterans of the 6th and 7th Divisions, 63,000 AIF who had not been out of the country and 280,000 militia. All were poorly equipped; there were practically no tanks, no aircraft and few fighting ships. Curtin faced the situation with a realism that won him many admirers. 'Without inhibitions of any kind,' he declared, 'I make it quite clear that (from now on) Australia looks to America, free of any pangs as to our traditional links or kinship with the United Kingdom.'

On orders from Washington General Douglas Macarthur flew in from the Philippines as supreme commander, South-West Pacific Area. In his wake followed an American fleet and thousands of troops, with equipment, munitions and aircraft. Australia went on to a full wartime footing. Civilian labour was directed to where it could be most useful - in munitions factories, in building airfields and a strategic north-south road through the continent's heart, on the docks. Food, clothing, petrol and all luxuries were rationed. (see home front) Taxes were heavily increased and the Commonwealth government took over all income taxation.

By now the enemy had moved into New Guinea and the Solomon Islands and invasion seemed imminent. Then came a dramatic change. On 7 and 8 May a Japanese fleet was intercepted and badly mauled in the Coral Sea; and early in June the enemy suffered a crushing defeat off Midway Island, losing four carriers, a cruiser and a destroyer. In between these battles, which were to prove crucial, two Japanese midget submarines penetrated Sydney harbour on the night of 31 May but succeeded only in torpedoing a ferry used as a depot ship before they were destroyed by depth-charges.

In the western desert the position remained critical. In June Tobruk fell after an heroic defence of fourteen months and the Afrika Corps reached to within sixty miles of Alexandria. The Australian 9th Division was moved from Syria to reinforce the Allies; and in October they played a vital part in General Montgomery's decisive break-through at El Alamein, which was to culminate seven months later in the surrender of all Axis troops in North Africa.

Through the second half of 1942 Japanese aggression in the south-west Pacific gradually waned in the face of stiffening Allied resistance. Guadalcanal, in the Solomons, became a major battle-ground; an enemy assault on Milne Bay, at the south-east tip of New Guinea, was repulsed with heavy losses; the threat to Port Moresby was removed when Australian troops drove the Japanese back over the Kokoda trail; and fierce fighting followed in the Buna-Gona area on the north coast of New Guinea. In a naval engagement off Guadalcanal one of four Allied cruisers sunk was HMAS Canberra. In the early months of 1943 there was a lull as both sides reorganized and built up their forces. During August and September Lae, Salamaua and Finschafen fell to the Allies and in the following month a strong Japanese counter-attack was defeated. By mid-1944 Japanese resistance in New Guinea had collapsed and in August Macarthur was able to move his headquarters north from Brisbane to Hollandia, in Dutch New Guinea. Then began the slow but inexorable process of flushing the Japanese out of the many islands they had occupied.

Although much desperate fighting was still to come in both the European and Pacific theatres there was little real doubt now about the eventual outcome. On 1 May 1945 Russian troops entered the ruins of Berlin and six days later the Germans surrendered unconditionally. Against what were by this time overwhelming odds the Japanese held out for another three months but they would have been wiser to accept the inevitable. Early in August a new and horrifying element was introduced when atomic bombs obliterated Hiroshima and Nagasaki and on 15 August on orders from the Emperor, Japan surrendered and the war was over. Because of the different character of the fighting Australian losses had been only about a third of those of the First World War - 21,000 dead and 58,000 other casualties. But psychologically the effect had been much more profound. Australia had emerged from dependent adolescence and was now, in her own right, an adult nation.