Iron Brigade The Iron Brigade , also known as the Iron Brigade of the West or the Black Hat Brigade , was an infantry brigade in the Union Army of the Potomac during the American Civil War . Although it fought entirely in the Eastern Theater , it was composed of regiments from Western states ( states that are today considered Midwestern ) . Noted for its strong discipline , its unique uniform appearance , and its tenacious fighting ability , the Iron Brigade suffered the highest percentage of casualties of any brigade in the war . The nickname " Iron Brigade " , with its connotation of fighting men with iron dispositions , was applied formally or informally to a number of units in the Civil War and in later conflicts . The Iron Brigade of the West was the unit that received the most lasting publicity in its use of the nickname . Brigade nickname . The Iron Brigade initially consisted of the 2nd , 6th , and 7th Wisconsin Volunteer Infantry Regiment s , the 19th Indiana , Battery B of the 4th U . S . Light Artillery , and was later joined by the 24th Michigan . This composition of men from three Western states led it to be sometimes referred to as the " Iron Brigade of the West " . They were known throughout the war as the " Black Hats " because of the black 1858 model Hardee hat s issued to Army regulars , rather than the blue kepi s worn in most other units . The all - Western brigade earned its famous nickname while under the command of Brig . Gen . John Gibbon , who led the brigade in its first battle at Brawner ' s Farm ( Gainesville ) on August 28 , 1862 , a prelude to the Second Battle of Bull Run , where it stood up against attacks from a superior force under Maj . Gen . Thomas J . " Stonewall " Jackson . The designation " Iron Brigade " is said to have originated during the brigade ' s action at Turners Gap , during the Battle of South Mountain , a prelude to the Battle of Antietam in September 1862 . Maj . Gen . Joseph Hooker , commanding I Corps , approached Army of the Potomac commander Maj . Gen . George B . McClellan , seeking orders . As the Western men advanced up the National Road , forcing the Confederate line all the way back to the gap , McClellan asked , " What troops are those fighting in the Pike ? " Hooker replied , " [ Brigadier ] General Gibbon ' s brigade of Western men . " McClellan stated , " They must be made of iron . " Hooker said that the brigade had performed even more superbly at Second Bull Run ; to this , McClellan said that the brigade consisted of the " best troops in the world " . Hooker supposedly was elated and rode off without his orders . There are a few stories related to the origin , but the men immediately adopted the name , which was quickly used in print after South Mountain . Brigade history . The unit that became known as the Iron Brigade was activated on October 1 , 1861 , upon the arrival in Washington , D . C . , of the 7th Wisconsin . It was combined into a brigade with the 2nd and 6th Wisconsin , and the 19th Indiana , under the command of Brig . Gen . Rufus King . The governor of Wisconsin , Alexander Randall , had hoped to see the formation of an entirely Wisconsin brigade , but the Army unwittingly frustrated his plans by transferring the 5th Wisconsin from King ' s brigade and including the Hoosiers instead . This brigade was initially designated the 3rd Brigade of Maj . Gen . Irvin McDowell ' s division of the Army of the Potomac , and then the 3rd Brigade , I Corps . McDowell ' s I Corps did not join the bulk of the Army of the Potomac in the Peninsula Campaign . In June 1862 it was redesignated the III Corps of Maj . Gen . John Pope ' s Army of Virginia . Now under the command of John Gibbon , a regular Army officer from North Carolina who chose to stay with the Union , King ' s brigade was designated the 4th Brigade , 1st division , III Corps , and it saw its first combat in the Northern Virginia Campaign . Almost immediately following the Union defeat in the Second Battle of Bull Run , the III Corps was transferred back to the Army of the Potomac and redesignated the I Corps , under the command of Joseph Hooker ; Gibbon ' s brigade became the 4th Brigade , 1st Division , I Corps . The 24th Michigan joined the brigade on October 8 , 1862 , prior to the Battle of Fredericksburg in December . On February 27 , 1863 , the brigade , now under the command of Brig . Gen . Solomon Meredith , was redesignated the 1st Brigade , 1st Division , I Corps . The brigade commanders , disregarding temporary assignments , were : The Iron Brigade lost its all - Western status on July 16 , 1863 , following its crippling losses at Gettysburg , when the 167th Pennsylvania was incorporated into it . However , the brigade that succeeded it , which included the survivors of the Iron Brigade , was commanded by : In June 1865 , the units of the surviving brigade were separated and reassigned to the Army of the Tennessee . The brigade fought in the Second Bull Run , Antietam , Fredericksburg , Chancellorsville , Gettysburg , Mine Run , Overland , Richmond - Petersburg , and Appomattox campaigns . The brigade took pride in its designation , " 1st Brigade , 1st Division , I Corps " , under which it played a prominent role in the first day of the Battle of Gettysburg , July 1 , 1863 . It repulsed the first Confederate offensive through Herbst ' s Woods , capturing much of Brig . Gen . James J . Archer ' s brigade , and Archer himself . The 6th Wisconsin ( along with 100 men of the brigade guard ) are remembered for their famous charge on an unfinished railroad cut north and west of the town , where they captured the flag of the 2nd Mississippi and took hundreds of Confederate prisoners . The Iron Brigade , proportionately , suffered the most casualties of any brigade in the Civil War . For example , 61 % ( 1 , 153 out of 1 , 885 ) were casualties at Gettysburg . Similarly , the 2nd Wisconsin , which suffered 77 % casualties at Gettysburg , suffered the 3rd highest total throughout the war ; it was third behind the 24th Michigan ( also an Iron Brigade regiment ) as well as the 1st Minnesota in total casualties at Gettysburg . The Michigan regiment lost 397 out of 496 soldiers , an 80 % casualty rate . The 1st Minnesota Regiment actually suffered the most casualties of any unit in the Civil War during the battle of Gettysburg losing 216 out of 262 men ( 82 % ) on day 2 of Gettysburg . Other Iron Brigades . There have been other brigades known by the same nickname . Use of the " Iron Brigade " name is not taken lightly in the U . S . Army , and the present - day units that have taken " Iron Brigade " as their nickname have proven themselves in battle as worthy to hold the name .