The Gallipoli Campaign, fought between the April of 1915 and the January of 1916 on the Gallipoli peninsula, was perhaps the most major military excursion into the Ottoman empire during the length of World War I, and the allied defeat was a contributing factor to the wars continuation until its end in November 1918.
During this conflict, the trench warfare on the hills of the peninsula reached stalemate, and all subsequent allied moves to end it failed and in the August of 1915, the last chance at victory came at the landing at Sulva Bay. Being part of the larger coordinated allied efforts to break the deadlock, the landing at Sulva was a disaster, brought about primarily by the British Lieutenant-General Frederick Stopford. His inability to deal with the situation at hand left the campaign in ruins after his failure to defeat the relatively light opposition.
However, during military's decision of who would lead the landing, two other important names appeared; Julian Byng, a well respected commander who fought at Ypres, and Henry Rawlinson, an equally respected commander who too fought on the Western Front, both of which had far more knowledge of warfare than Stopford ever had. In OTL, these two suggestions were struck down by both Field Marshall Herbert Kitchener, as well as the Commander of the Mediterranean Expeditionary Forces, Sir Ian Hamilton.
In this timeline however, one of the commanders, Julian Byng, is chosen to lead the charge at Sulva Bay, effectively commanding the troops to victory of the Turk, changing the course of the war forever...