[1][2] Captain King continued to serve on frontier duty at various posts and gained the nickname "Iron Bull" together with a reputation as hard-working and competent officer.

[1] In March 1861 he was stationed at San Antonio, Texas, and in defiance of the rising Texan rebels, he helped organizing Camp Green Lake and sailed with nine companies of Regulars safely to New York.

There the regular detachments were grouped as part of the brigade of Lovell Rousseau in Alexander McDowell McCook's 2nd Division of the Army of the Ohio.

[4] With additional reinforcements arriving Major King, as senior officer present, was assigned to command all regular forces in the brigade; in December already made up of 13 companies from the 15th, 16th and 19th regiments.

[7] Shortly after the battle command of the, again enlarged, Regular Detachment developed on Lt. Col. Oliver L. Shepherd and King returned to his regiment.

When Maj. Gen. William Rosecrans took command of the new Army of the Cumberland, he took King and his battalion as his headquarters guard and personal escort; but returned them to the detachment when he formed the Regular Brigade in December.

[9] Only days later the new brigade, part of Rouseau's Division in the XIV Corps, would distinguish itself in the bloody Battle of Stones River, though suffering severe casualties.

[13] While the Tullahoma Campaign unfolded King was unfit to command his men in the Battle of Hoover's Gap as his hand hadn't fully healed yet.

[19] For the greater part of the Atlanta Campaign King would command the division due to Gen. Richard W. Johnson first being wounded and then being assigned to lead the corps.