The 5th Division was an infantry division of the Australian Army which served during the First and Second World Wars. The division was formed in February 1916 as part of the expansion of the Australian Imperial Force infantry brigades. In addition to the existing 8th Brigade were added the new 14th and 15th Brigades, which had been raised from the battalions of the 1st and 2nd Brigades respectively. From Egypt the division was sent to France and then Belgium, where they served in the trenches along the Western Front until the end of the war in November 1918. After the war ended, the division was demobilised in 1919.

The division was re-raised as a Militia formation during the Second World War, and was mobilised for the defence of North Queensland in 1942, when it was believed that the area was a prime site for an invasion by Japanese forces. Most of the division was concentrated in the Townsville area, although the 11th Brigade was detached for the defence of Cairns and Cape York. In 1943, the division took part in the final stages of the Salamaua–Lae campaign, in New Guinea, and then later in 1944 captured Madang during the Huon Peninsula campaign. In 1944–1945, the division was committed to the New Britain campaign, before being relieved in July 1945. The division was disbanded in September 1945 following the end of the war.

In early 1916, following the unsuccessful Gallipoli campaign, the Australian government decided to expand the size of the Australian Imperial Force (AIF). At the time there were two Australian divisions in Egypt: the 1st and 2nd. The 3rd Division was raised in Australia, while the 1st Division was split up to provide a cadre upon which to raise the 4th and 5th Divisions. The 14th and 15th Brigades were formed from the 1st and 2nd Brigades, while the division's third brigade, the 8th, comprised newly formed battalions that had recently arrived from Australia and were unattached at divisional level. On formation at Tel el Kebir in February 1916, the 5th Division joined II Anzac Corps, and its main element was its three infantry brigades: the 8th, 14th and 15th. Upon formation, each brigade consisted of around 4,000 personnel, organised into four infantry battalions.

When the more experienced I Anzac Corps embarked for France at the end of the month, they took most of the available artillery pieces and trained artillery personnel, leaving the II Anzac divisions to train new artillery batteries from scratch, a process that would take three months. Major-General James McCay, formerly commander of the Australian 2nd Infantry Brigade, assumed command of the division on 21 March 1916, after returning from Australia, having been wounded during the Gallipoli campaign.

After the dispatch of the 1st and 2nd Divisions to France, responsibility for the defence of the Suez Canal against an expected Turkish attack passed to the remaining two Australian divisions. The 5th Division was allocated to the defence of the canal around Ferry Post. Moving by train to Moascar, and then by foot to Ferry Post, the 8th Brigade moved in to position by 27 March. Meanwhile, the remainder of the division's infantry – the 14th and 15th Brigades – were to complete the move on foot, a march of 57 kilometres (35 mi) from the Anzac camp at Tel el Kebir. McCay voiced some concerns about the march to his superiors, but followed the order and his actions during the march, and words afterwards, later soured relations between the divisional commander and the soldiers. Taking three days over soft sand and in extreme heat (with temperatures up to 100 °F (38 °C)) the men in the two brigades suffered severely and the march was completed in disarray with many suffering heat illness; many were helped in from the desert by a neighbouring New Zealand unit who volunteered to provide assistance upon learning of the situation.

Throughout late March to the end of May, concurrently with completing the process of training and equipping, the division's brigades rotated through the positions forward of Ferry Post. Finally, at the end of the month, the British 160th Brigade arrived, relieving the Australians. Throughout June, the division returned to Moascar, where reinforcements were received to bring units up to their authorised strengths in preparation for their transfer to Europe, to join the fighting on the Western Front. In the middle of the month, they moved by train to Alexandria and embarked on a number of troopships.

The 5th Division began arriving in France in late June 1916, landing in Marseille, the last of the four Australian divisions from Egypt to do so (although the 3rd Division, which sailed from Australia, arrived last in February 1917). At this time the Battle of the Somme was underway and going badly for the British. The divisions of I Anzac Corps, which had been acclimatising in the quiet sector near Armentières since April 1916, had been dispatched to the Somme as reinforcements, and so the 4th and 5th Divisions, which formed part of II Anzac Corps under Lieutenant General Alexander Godley, took their place at Armentières. The 4th Division subsequently occupied the front, while the 5th Division remained in reserve, completing training around Blaringhem, until 8 July, when it was called to take over from the 4th Division around Bois-Grenier, which also began preparations to move south. The 8th and 15th Brigades arrived on the night of 10/11 July, while the 14th moved into position on 12 July.

The result of this move was that the 5th Division, the most inexperienced of the Australian divisions in France, would be the first to see major action, doing so in the Battle of Fromelles, a week after going into the trenches. As the Germans had been reinforcing their Somme front with troops from the north, the British planned a demonstration, or feint, to try to pin these troops to the front.