On 19th February, 1915, the British attacked the Turkish forts at the Dardanelles. The assault started with a long range bombardment followed by heavy fire at closer range. As a result of the bombardment the outer forts were abandoned by the Turks. The minesweepers were brought forward and managed to penetrate six miles inside the straits and clear the area of mines.

Further advance up into the straits was now impossible. The Turkish forts were too far away to be silenced by the Allied ships. The minesweepers were sent forward to clear the next section but they were forced to retreat when they came under heavy fire from the Turkish batteries.

Winston Churchill, First Lord of the Admiralty, became impatient about the slow progress that Admiral Sackville Carden was making and demanded to know when the third stage of the plan was to begin. Admiral Carden found the strain of making this decision extremely stressful and began to have difficulty sleeping. On 15th March, Carden's doctor reported that the commander was on the verge of a nervous breakdown. Carden was sent home and replaced by Vice-Admiral Sir John de Robeck, who immediately ordered the Allied fleet to advance up the Dardanelles Straits.

On 18th March eighteen battleships entered the straits. The fleet included Queen Elizabeth, Lord Nelson, Agamemmon, Inflexible, Ocean, Irresistible, Prince George and Majestic from Britain and the Gaulois, Bouvet and Suffren from France. At first they made good progress until the Bouvet struck a mine, heeled over, capsized and disappeared in a cloud of smoke. Soon afterwards two more ships, Irresistible and Ocean hit mines. Most of the men in these two ships were rescued but by the time the Allied fleet retreated, over 700 men had been killed. Overall, three ships had been sunk and three more had been severely damaged.

Vice-Admiral Sir John de Robeck now informed Winston Churchill that he could not capture the Gallipoli peninsula without the help of the army. General Ian Hamilton, commander of the troops on the Greek island of Lemnos, who had watched the failed navy operation, agreed and plans were now made for full-scale landings at Gallipoli.

Leaders of the Greek Army informed Kitchener that he would need 150,000 men to take Gallipoli. Lord Kitchener concluded that only half that number was needed. Kitchener sent the experienced British 29th Division to join the troops from Australia, New Zealand and French colonial troops on Lemnos. Information soon reached the Turkish commander, Liman von Sanders, about the arrival of the 70,000 troops on the island. Sanders knew an attack was imminent and he began positioning his 84,000 troops along the coast where he expected the landings to take place.

The attack that began on the 25th April, 1915 established two beachheads at Helles and Gaba Tepe. Another major landing took place at Sulva Bay on 6th August. However, attempts to sweep across the peninsula ended in failure. By the end of August the Allies had lost over 40,000 men. General Ian Hamilton asked for 95,000 more men, but although supported by Winston Churchill, Kitchener was unwilling to send more troops to the area.

On 14th October, Hamilton was replaced by General Munro. After touring all three fronts Munro recommended withdrawal. Lord Kitchener, who arrived two weeks later, agreed that the 105,000 men should be evacuated. The operation began at Sulva Bay on 7th December. The last of the men left Helles on 9th January, 1916.

About 480,000 Allied troops took part in the Gallipoli campaign. The British had 205,000 casualties (43,000 killed). There were more than 33,600 ANZAC losses (over one-third killed) and 47,000 French casualties (5,000 killed). Turkish casualties are estimated at 250,000 (65,000 killed).