The 5th Missouri Infantry Regiment evolved from a network of several unofficial pro-Unionist militia groups formed semi-secretly in St. Louis in the early months of 1861 by Congressman Francis Preston Blair Jr. and other Unionist activists.
Although initially without any official standing, beginning on April 22, 1861, the militia regiments Blair helped organize were sworn into Federal service at the St. Louis Arsenal by Captain John Schofield acting on the authority of President Lincoln.
Sigel's 2nd Brigade initially had significant success, attacking Confederate cavalry on the southeast corner of the southern camps (at the Sharp Farm).
However, Sigel positioned his artillery badly (behind the military crest of the ridge) and cautioned his men against accidentally firing on Federal troops he expected to be advancing south down the Wire Road (the 1st Iowa Infantry was uniformed in grey).
At this point, Confederate Brigadier Ben McCulloch lead an attack south down the Wire Road, with the respected Third Louisiana Infantry in the fore.