After a winter of relative inactivity, the British commander in Mesopotamia, General Marshall, resumed the offensive on his eastern flank in March, defeating the Ottoman forces. On 27 April, he ordered his western flank to march on Kirkük in northern Iraq. Their first enemy encounter was at Kulawand, meeting little resistance; but the waterlogged conditions impeded the British cavalry and motorized vehicles. Aerial reconnaissance then established the Ottoman forces entrenched along a 4-mile (11-km) line from Tuz Khurmatu to Yanija Kuchuk, blocking the road to Kirkuk from behind the Aq Su River. While infantry made a frontal assault under cover of artillery fire, the mounted 13th Hussars, and 21st and 22nd Cavalry circled behind enemy lines from the west, cutting off their line of retreat along the road to Tauq. Within a few hours, the Ottoman forces had surrendered, 1,200 prisoners being taken: the way to Kirkuk was now clear.