The Ottoman 5th Army defending the peninsula included a relatively junior but unusually confident officer named Mustafa Kemal, commanding the 19th Division. Kemal had served on this same peninsula during the Balkan Wars a few years earlier and knew the ground intimately. He predicted correctly that the likely landing sites were at the southern tip of the peninsula and at a bay on the Aegean coast near Gaba Tepe. Sanders placed Kemal's division in reserve, ready to move quickly to wherever the crisis broke. That decision would prove decisive.

The landings were planned for 23 April but bad weather pushed them to 25 April 1915. In the pre-dawn darkness, the covering force of the ANZAC corps embarked from battleships and destroyers into open boats and was towed toward the Aegean shore. Undetected currents or a navigational error pushed the boats about two kilometres too far north, depositing the first wave not on the gently shelving beach they had rehearsed for, but beneath cliffs and steep ravines that no plan had anticipated. The Australians scrambled ashore under fire from the two Ottoman companies holding the high ground above them.

The defenders were too few to throw the Australians back into the sea, but the broken terrain, the scrub-covered ravines, and the confusion of landing in the wrong place meant that the covering force could not advance in any coordinated direction. Small groups pushed inland and some reached the second ridge, but they became separated and lost contact with each other. By mid-morning, Kemal had assessed the situation, recognised that whoever held the heights of Chunuk Bair and Sari Bair would control the entire lodgement, and ordered his division forward. His instruction to his troops became one of the defining utterances of the campaign: he told them he was not ordering them to fight, but to die. In the time that passed until they died, other troops and commanders would come forward to take their places.

The Ottoman 57th Infantry Regiment obeyed that order literally. By morning's end, every man in the regiment was either killed or wounded, but the heights held. The Australian right flank was driven in at mid-morning, and through the afternoon the left flank was pushed back from the high ground. By evening, the senior Australian commanders on the beach were recommending immediate re-embarkation. Birdwood agreed, but the navy told him it could not be done. Hamilton, from his command ship offshore, ordered the troops to dig in instead. They dug, and stayed, in a perimeter less than two kilometres long. ANZAC casualties on that first day were around two thousand killed or wounded.

At Cape Helles, at the southern tip of the peninsula, the British 29th Division landed on five beaches in an arc. At most beaches the fighting was fierce, but at two of them it was a massacre. At the beach beneath the old Seddülbahir fortress, a converted collier called River Clyde was run aground so that soldiers could disembark along ramps. The troops emerged one by one through narrow openings and were cut down by Ottoman defenders in the fortress above. Of the first two hundred soldiers to step onto those ramps, twenty-one reached the beach. At the next beach along, the Lancashires landed in open boats and took six hundred casualties from a thousand men, yet still managed to overwhelm the defenders. Six Victoria Crosses were awarded among the Lancashires that day; six more among the infantry and sailors at the fortress beach. The Ottoman defenders were too few to stop the landings entirely, but they were enough to stop the advance.

Within days it was clear that the swift campaign Hamilton had envisioned was not going to happen. Ottoman reinforcements arrived steadily, and the possibility of a rapid advance on the forts at Kilitbahir faded. The fighting at both Helles and ANZAC Cove settled into the pattern that already scarred the Western Front: trench lines separated by no man's land, artillery exchanges, and infantry attacks that gained hundreds of yards at the cost of thousands of lives.

The first attempt to capture the village of Krithia, in the hills above the Helles beaches, was launched on 28 April. The plan was too complex, the troops were exhausted, and the Ottomans stopped the advance halfway up the peninsula with three thousand Allied casualties. A second attempt on Krithia in early May involved twenty thousand men, including Australians and New Zealanders transferred from Anzac. It failed again. A third attempt on 4 June failed as well, costing the British alone forty-five hundred casualties from twenty thousand men engaged. Krithia was never taken.

On 19 May, the Ottomans launched their own major counter-attack at Anzac, sending forty-two thousand men against the seventeen thousand Australians and New Zealanders holding the perimeter. The attack had been spotted by British aircraft the previous day, so it met prepared defenders. The Ottomans suffered roughly thirteen thousand casualties, three thousand of them killed, while the ANZAC force lost fewer than two hundred dead and under five hundred wounded. The dead lay thick in no man's land, and the smell became unbearable. On 24 May, both sides agreed to a truce to bury them. For a few hours, men who had been killing each other walked together in the open, and Private Laidlaw of an Australian field ambulance noted that the scene felt so unnaturally quiet he felt like making a row himself.

At sea, the Allied submarines were fighting their own campaign inside the Dardanelles and the Sea of Marmara. The Australian submarine AE2, under Lieutenant Commander Stoker, had penetrated the straits on the night before the landings and reached the Sea of Marmara, where it cruised for five days before being forced to surface, damaged by Ottoman fire, and scuttled. Its achievement showed that the passage was possible. The British submarine E14, under Lieutenant Commander Boyle, then spent three weeks in the Marmara, sinking four ships including a transport carrying six thousand Ottoman troops, and was awarded the Victoria Cross. The submarine E11 later entered Constantinople Harbour and fired on ships alongside the arsenal. These operations were the single consistent Allied success of the campaign, forcing the Ottomans to abandon the sea as a supply route.

By summer, Hamilton had a new plan. The original landing zones were too confined to allow any breakout. He would land two fresh divisions at Suvla Bay, eight kilometres north of Anzac, and simultaneously launch a major assault from the ANZAC perimeter toward the Sari Bair heights that had been the objective on the first day. If Chunuk Bair and the high ground of Hill 971 could be taken, the Allies would command the peninsula and the whole campaign might still be salvaged.

The Suvla landing on the night of 6 August went in against light opposition. The Ottoman defenders were thin on the ground and the beach was taken with little difficulty. But the British commander at Suvla, Lieutenant General Stopford, had set himself limited initial objectives and then failed to press his men forward. The Ottomans occupied the Anafarta Hills overlooking the bay before the British moved to seize them. What had been an open door closed, and Suvla became yet another static front.

At the ANZAC perimeter, the assault on Chunuk Bair came agonisingly close. The New Zealand Infantry Brigade climbed through the night and by dawn on 7 August was within five hundred metres of the peak. They could not quite reach it. The following morning they seized the summit, and for two days the New Zealanders held a position that might have cracked the entire Ottoman defence open. Then on 10 August, Mustafa Kemal led an Ottoman counter-attack that swept them off the heights. Of the 760 men of the Wellington Battalion who had reached the summit, 711 became casualties. The best chance of an Allied victory at Gallipoli died on that ridge.

The attack at the Nek, where the Australian 3rd Light Horse Brigade charged on a narrow front to coincide with the New Zealand push, became one of the campaign's most remembered disasters. The artillery barrage lifted seven minutes too early, alerting the Ottoman defenders. The Light Horsemen went over the parapet anyway, wave after wave, into concentrated fire. They had no chance. The attack was a costly failure that achieved nothing and cost the brigade heavily. The final British attempt to revive the offensive, in late August at Scimitar Hill, also failed. Hamilton went onto the defensive and requested another ninety-five thousand reinforcements. He received roughly a quarter of that number.

Through the long summer, the campaign's other enemy was invisible. The heat, the overcrowded beaches, the unburied dead, and the flies created conditions in which disease spread without check. Dysentery swept through the Allied trenches at both Anzac and Helles. Typhoid and diarrhoea added to the toll. The British official historian recorded that over ninety thousand soldiers of the British Empire were evacuated for illness during the campaign, and that nearly a hundred and fifty thousand British troops fell sick, of whom almost four thousand died from disease alone. The proportion of sick to battle casualties was far higher at Gallipoli than on the Western Front.

The Ottomans suffered equally. Liman von Sanders estimated sixty-six thousand Ottoman dead from all causes, with more than two hundred thousand casualties in total. Disease killed on both sides without distinguishing between victor and defeated. The front settled into a grim routine of sniping, grenade attacks, and tunnelling. The Ottomans began mining the ANZAC lines in late May, detonating a charge near Quinn's Post and attacking with a battalion. The Australians were briefly driven back, then counter-attacked and recaptured the ground. The pattern would be repeated many times.

Hamilton was dismissed in October 1915 after critical press reports, including those smuggled out by the journalist Keith Murdoch, reached London. His replacement, Lieutenant General Monro, arrived and within days recommended evacuation. Kitchener, the Secretary of State for War, travelled to the eastern Mediterranean himself in early November and, after consulting the corps commanders, agreed. The British Cabinet confirmed the decision to evacuate in early December.

The evacuation was, in the end, the campaign's one genuine operational success. It was also the thing planners had dreaded most, fearing the narrow beaches and the proximity of Ottoman trenches would produce thirty thousand casualties as troops tried to withdraw. The engineers and soldiers tasked with the operation proved more inventive than anyone had expected. Troop numbers at Anzac and Suvla were slowly reduced from early December while elaborate ruses maintained the appearance of normal activity.

A private soldier named William Scurry rigged a self-firing rifle: water dripped into a pan attached to the trigger, and the rifle fired at intervals long after the man who set it had gone. At Anzac Cove, troops maintained absolute silence for an hour or more to accustom the Ottomans to quiet; when the Ottomans sent men forward to investigate, the Anzacs opened fire and drove them back. The same silence on the night of the real evacuation therefore drew no response. A mine was detonated at the Nek, killing seventy Ottoman soldiers, and the last Australian troops slipped away before dawn on 20 December 1915 without a single casualty.

Helles was held a little longer, and the Ottomans were more alert to signs of withdrawal. Sanders launched an infantry and artillery attack on the British lines on 7 January 1916 but it failed. That night and the next, under cover of a naval bombardment, the British troops fell back to the beaches. Makeshift piers were used to board the boats. The last British troops departed from the beach known as Lancashire Landing at four in the morning on 8 January. The Newfoundland Regiment, part of the rearguard, withdrew on 9 January. The remnants of the Plymouth Battalion of Royal Marine Light Infantry, among the first to land, were the last to leave the peninsula.

The numbers that followed the evacuation took years to compile and are still disputed. In the Gallipoli campaign, more than a hundred thousand men were killed outright, with estimates of Ottoman dead ranging from fifty-six thousand to nearly ninety thousand, and Allied dead around fifty-three thousand. Total casualties on both sides, including wounded and sick, approached half a million. Of the roughly eight thousand seven hundred Australians killed, just eleven of the thousand or so men from the Dublin Fusiliers who had landed at V Beach survived the campaign unscathed. The New Zealand official history counted two thousand seven hundred and twenty-one New Zealanders killed, roughly a quarter of all those who had landed.

The political consequences in Britain were immediate and severe. Churchill had been the campaign's most visible champion. He was demoted from First Lord of the Admiralty as the price of Conservative entry into a coalition government, reduced to a sinecure, and then resigned in November 1915 to command an infantry battalion on the Western Front. The campaign haunted him for decades, and the question of whether he had been right about the strategic concept but undone by incompetent execution would follow him to the end of his career.

Hamilton's military career ended with his recall to London in October 1915. Stopford was also dismissed. The Dardanelles Commission was established to investigate the failure, its first report appearing in 1917 and its final report in 1919. The Commission concluded that success had been possible only if the government had made the expedition its absolute priority, and that Hamilton had been over-optimistic from the start. Hamilton, the report noted, had made devious attempts to influence witnesses and obtain leaks from the Commission's deliberations. He never received another army appointment.

For the Ottomans, the campaign had the opposite effect. It confirmed their ability to defeat a major Allied assault, boosted morale across the empire, and elevated Mustafa Kemal to national prominence. The confidence gained at Gallipoli was real, even if it could not sustain the empire through the rest of the war. In Mesopotamia the following year, an Ottoman force surrounded and captured an entire British expedition at Kut, a defeat that owed something to the spirit of resistance hardened on the Gallipoli ridges.

The Gallipoli campaign left marks that outlasted the war, the empire that had fought it, and the generation that had survived it. For Australia and New Zealand, the landings on 25 April 1915 became the founding myth of national identity in a way that no subsequent event has displaced. The date was first commemorated unofficially in 1916, recognised as a public holiday in all Australian states by 1923, and observed as a national holiday in New Zealand in the same decade. Organised marches by veterans began in 1925. The dawn service at Gallipoli itself drew over ten thousand people to the seventy-fifth anniversary, with political leaders from Turkey, New Zealand, Britain, and Australia standing together on the beach where the boats had come in.

In Turkey, the battle is remembered primarily for 18 March, the day the Allied fleet was turned back, a date commemorated with ceremonies even though it is not a public holiday. The phrase that entered common speech, roughly translated as 'Çanakkale is impassable', expressed a pride that went beyond military victory. The campaign's deepest significance for Turkey lies in the figure of Mustafa Kemal: the young divisional commander who held Chunuk Bair went on to lead the Turkish War of Independence after the war's end, dissolved the Ottoman sultanate, and in 1923 became the founder and first president of the Republic of Turkey. Gallipoli did not make him, but it was where the world first saw what he was.

The military lessons were studied for decades. The catastrophe of opposed amphibious landings, the failures of coordination between navy and army, the underestimation of a defending force, the cost of delay: all of these were absorbed, painfully, by planners who faced similar problems in the Second World War. The landings in the Pacific, in Italy, and ultimately at Normandy in June 1944 were shaped by what had gone wrong on the Gallipoli beaches in April 1915. The campaign became, in the words of one analyst, a focal point for the study of amphibious warfare in both Britain and the United States for the entire period between the wars.

There are thirty-one Commonwealth War Graves cemeteries on the Gallipoli peninsula today, spread between Helles, Suvla, and Anzac. For many of those killed at sea or buried in ground that could not be held, there is no known grave; their names are recorded on memorials to the missing. The Lone Pine Memorial stands above the beach where the Australians dug in on that first night, listing the names of men whose bodies were never recovered. The Turkish 57th Regiment, which died to the last man holding the heights above the Anzac landing, is commemorated near Quinn's Post. The dead of both sides lie within a few hundred metres of each other on a peninsula that neither side could hold and neither side could abandon.

What Gallipoli ultimately cost was not just the lives counted in the official histories. It cost the confidence of a generation in the competence of those who sent them. It cost Churchill nearly a decade of political influence. It cost the Ottoman Empire one of its last great reserves of military strength, even in victory. And it gave Australia, New Zealand, and Turkey something harder to measure: a shared conviction, born in the same eight months of fighting, that who they were as nations had been decided on those cliffs and ridges, in the dark, before anyone back home had finished their breakfast.