Gallipoli Campaign (April 25, 1915-January 8, 1916), major land and sea operation of World War I, in which British, French, Australian, and New Zealand forces unsuccessfully attempted an invasion of Turkey. The action was confined to the Dardanelles Strait and the tip of the Gallipoli (Gelibolu) Peninsula near the capital, Constantinople (İstanbul).

The campaign had its origins in the growing dissatisfaction in some British political and military circles over the progress of the campaign on the Western Front. Winston Churchill, First Lord of the Admiralty, in particular, argued for a naval assault on Turkish positions on the Dardanelles Straits, in order to relieve Turkish pressure on Russian forces in the Caucasus and to open up a direct supply route through the Black Sea to the hard-pressed Russian front. Other parties to the plan were the British munitions minister David Lloyd George, General Herbert H. Kitchener, and Admiral Sackville H. Carden. When the naval bombardment of the Turkish positions on the Straits failed abysmally in February, the decision was taken to commit land forces.

The British and French forces available were deemed insufficient to the task, and the decision was therefore taken to use the Australian and New Zealand Army Corps (hence the acronym Anzac), then training in Egypt prior to going to France, in a secondary role. British landings at Cape Helles on April 25 made little headway, while the Anzac forces further north landed at the wrong beach and encountered stiff Turkish resistance in rugged terrain. Excessive caution and timorous leadership by the British commander, Sir Ian Hamilton, resulted in several lost initiatives. The campaign remained virtually static until a reinforced assault was undertaken in August to protect a British landing at Suvla Bay, north of the main Anzac positions. Undue caution by British commanders and the difficulties of the terrain combined with vigorous Turkish resistance under the leadership of Mustapha Kemal (later Kemal Atatürk, President of Turkey), with the German commander, Otto Liman von Sanders, to render progress impossible, and a stalemate ensued.

New Zealand forces briefly captured the heights of Chunuk Bair, from where the Straits could be seen in full view, but were forced back under Turkish pressure. Conditions on the peninsula deteriorated and casualties mounted, as much from disease as from the close proximity of the battle lines. Inadequate preparation had been made for the provision of medical services, and wounded and sick troops were evacuated from the peninsula in appalling conditions. Hamilton was replaced by Sir Charles Monro, who was sent to evaluate the situation. Finally, in December, the decision was taken to withdraw all Allied forces: the evacuation was carried out without a single casualty, making it the only successful part of the failed operation. Total casualties for the campaign were: British and imperial forces, 205,000 out of a total of 410,000; French, 47,000 out of 79,000; and Turkish, about 250,000 out of 500,000. For Australia, the casualty rate was 27,594 (7,594 dead) out of a total of 50,000; for New Zealand 7,247 (2,701 dead) out of 8,556.

The failure of the Gallipoli campaign destroyed several reputations, including for a time Churchill’s, and was to haunt him for decades to come. In Australia and New Zealand it nurtured, on the one hand, the legend of the Anzac soldier—brave, resourceful, and individualistic—and on the other the myth of an incompetent and callous British High Command that was prepared to sacrifice colonial troops. April 25 has become a central day of commemoration and remembrance in both New Zealand and Australia, a celebration (especially in Australia) of what is claimed to be the day that the young commonwealth became a true nation. On Anzac Day, the dawn landing at Anzac Cove is commemorated by dawn services, which are followed by huge marches of veterans from all wars; thousands of Australians and New Zealanders flock to the Gallipoli peninsula. Overall the Gallipoli campaign was a military disaster. Despite this, it did weaken the Turks sufficiently to facilitate the British seizure of Palestine in 1917, and distracted the Germans from their 1915 plan to begin another offensive in France.