The Allied forces along this line were organized into three army groups. In the north, from the North Sea to a point about 10 miles (16 km) north of Cologne, was the 21st Army Group commanded by Field Marshal Bernard Montgomery. Within 21st Army Group the Canadian 1st Army (under Harry Crerar) held the left flank of the Allied line, with the British 2nd Army (Miles C. Dempsey) in the center and the U.S. 9th Army (William Hood Simpson) to the south.