Political map of South & Southwest Asia 5 January 1916 (Siege of Kut): The British had consolidated control over the Persian Gulf at the start of the War (World War I) by invading southern Mesopotamia (Mesopotamian Campaign). In 1915 they decided to march on Baghdad and end the Ottoman threat to Persia (Persian Campaign). However, they had underestimated their opponents - the Ottomans not only repelled the British at Ctesiphon (Battle of Ctesiphon (1915)), but managed to trap their forces at Kut (Siege of Kut). Despite numerous relief attempts, the garrison of Kut was forced to surrender after a 147 day siege.