As the only waterway between the Black Sea in the east and the Mediterranean Sea in the west, the Dardanelles was a much-contested area from the beginning of World War I. The stakes for both sides were high: British control over the strait would mean a direct line to the Russian navy in the Black Sea, enabling the supply of munitions to Russian forces in the east and facilitating cooperation between the two sides. The Allies were also competing with the Central Powers for support in the Balkans, and the British hoped that a victory against Turkey would persuade one or all of the neutral states of Greece, Bulgaria and Romania to join the war on the Allied side. Finally, as British Foreign Secretary Edward Grey put it, the approach of such a powerful Allied fleet toward the heart of the Ottoman Empire might provoke a coup d’état in Constantinople, leading Turkey to abandon the Central Powers and return to its earlier neutrality.

Support from the rest of the British war command came none too soon for Winston Churchill (1874-1965), the British first lord of the admiralty (akin to the secretary of the U.S. Navy), who had long been a proponent of an aggressive naval assault against Turkey at the Dardanelles. Though others, especially the French military command, led by Joseph Joffre, argued that the navy should not strike until ground troops could be spared from the Western Front, Churchill pushed to begin immediately.

The attack, planned throughout the winter of 1915, opened on March 18, 1915, when six English and four French battleships headed toward the strait.

The Turks were aware that an Allied naval attack on the strait was a strong possibility, and with German help, had greatly improved their defenses in the region. Though the Allies had bombarded and destroyed the Turkish forts near the entrance to the Dardanelles in the days leading up to the attack, the water was heavily mined, forcing the Allied navy to sweep the area before its fleet could set forth. However, the minesweepers did not manage to clear the area completely: Three of the 10 Allied battleships (Britain’s Irresistible and Ocean, and France’s Bouvet) were sunk, and two more were badly damaged.

With half the fleet out of commission, the remaining ships were pulled back. Though Churchill argued for the attack to be renewed the next day, claiming, erroneously as it turned out, that the Turks were running low on munitions, the Allied war command opted to delay the naval attack at the Dardanelles and combine it with a ground invasion of the Gallipoli Peninsula, which bordered the northern side of the strait.

The Allied landing on Gallipoli, which took place on April 25, 1915, met with a fierce Turkish defense inspired by Turkish leader Mustafa Kemal (1881-1938), who was the future president of Turkey and later known as Ataturk, and directed skillfully by the German commander Otto Liman von Sanders. For the remainder of the year, Allied forces, including large contingents from Australia and New Zealand, were effectively held at the beaches where they had landed, hampered by cautious and ineffective leadership from their British commander, Sir Ian Hamilton. Hamilton was replaced near the end of 1915 by Charles Monro, who recommended that the Allies abandon the operation. The armies were fully evacuated by the end of January 1916.

The failure of the campaign at the Dardanelles and at Gallipoli resulted in heavy casualties—approximately 205,000 for the British Empire and 47,000 for the French (there were also 250,000 Turkish casualties)—and was a serious blow to the reputation of the Allied war command, including that of Churchill, who resigned his position with the admiralty after being demoted and headed to the Western Front to command a battalion.