The Allied forces attempted to capture the Dardanelles during the Gallipoli Campaign. The strait was the gateway between the Aegean Sea and the Sea of Marmara, leading onward to Constantinople and the Black Sea.
Beginning in February 1915, British and French warships tried to force their way through the strait and destroy Ottoman defenses. Mines, coastal artillery, and difficult currents stopped the naval assault. Allied troops then landed on the Gallipoli Peninsula in April to seize the defensive positions by land.
The campaign continued until the final evacuations in January 1916 and ended in an Ottoman victory. The Dardanelles are sometimes confused with the nearby Bosphorus, but the two are separate Turkish straits: the Dardanelles connects the Aegean to the Sea of Marmara, while the Bosphorus connects the Sea of Marmara to the Black Sea.