The Union strategy at Wilson's Creek called for a two-pronged surprise attack in which General Lyon's main column of about 4,000 men would strike the Confederate camps from the north while Colonel Franz Sigel's brigade of about 1,200 men attacked from the south, with the Confederate army to be crushed between the converging columns. The plan seemed effective at first, but the Union forces were outnumbered, and poor communications between Lyon and Sigel made coordination difficult. A line of advancing Rebels that the Federals mistook for reinforcements, the gray-clad 1st Iowa, charged and overran Sigel's position.