[2] At the outbreak of the American Civil War, McKee immediately worked to recruit a company of volunteers from the Lancaster area and was elected captain.

[2] The 2nd Wisconsin Infantry was assigned to the brigade of Colonel William Tecumseh Sherman in the Army of Northeastern Virginia.

[4]: 439  In the morning phase of the battle, they were part of Sherman's successful flanking attack which destabilized the Confederate left.

They received visits from President Abraham Lincoln, Secretary of State William H. Seward, and Wisconsin Governor Alexander Randall.

[1] McKee met the regiment at Island Number Ten on the Mississippi River, near New Madrid, Missouri, after the battle there.

[6]: 615 In June, the 15th Wisconsin departed Island Number 10, marching to Union City, Tennessee, and joining the division of General Robert Byington Mitchell.

The Battle of Perryville occurred on October 8, 1862, but the 15th Wisconsin Infantry and its division was located at a position south of the main battlefield.

Colonel McKee was put in command of an expedition to reconnoiter forage and terrain, and hunt Confederate guerillas.

He captured 47 prisoners, destroyed about 100 small arms, and burned two homes and a distillery which he believed were providing refuge to guerilla parties.

[6]: 617  Colonel William Carlin complimented McKee on the expedition, saying, "This handsome little success, which shows what good infantry can do under an enterprising leader, reflects much credit on all who were engaged in it.

[6]: 618  McKee took one company from each regiment of the brigade and led them directly at the enemy cannons, through brush and over hills, until they were close enough to open fire.

Colonel Heg, commanding the 15th Wisconsin Infantry, sought to stabilize the line and ordered his regiment to turn right to avoid being flanked.