Gallipoli Campaign, an Allied attempt in 1915, during World War I, to seize the Gallipoli Peninsula in Turkey and thus gain control of the Dardanelles strait, opening a supply route from the west to Russia through the Black Sea. A victory, the Allies thought, would also drive Turkey (an ally of Germany) out of the war. The campaign was a failure, doomed by poor planning in London and inept leadership in the field. As a result, Winston Churchill, first lord of the admiralty and principal supporter of the operation, was removed from office.

The first attempt to take the strait was by naval action alone. On March 18 several squadrons of British and French naval vessels sailed into the strait and began bombarding Turkish fortifications. The attack was called off when two battleships and a battle cruiser were sunk by mines. On April 25 Allied forces, commanded by General Ian Hamilton, attacked the peninsula. Turkish forces, under the command of a German general, Liman von Sanders, put up a strong defense. The Allied troops made no headway and had to dig in until more troops arrived in July. On August 6, a second attempt to take the peninsula failed.

Allied soldiers were evacuated beginning in December and ending on January 9, 1916. In all 410,000 British, Anzac (Australian and New Zealand Army Corps), and Indian troops participated, along with 70,000 French and North Africans. The Allied killed, wounded, ill, or taken prisoner numbered 252,000. Turkish casualties were 251,000.