The third 15th Arkansas Infantry—the one commanded by Col. Squire Boone and known as the 15th (Northwest) Arkansas Regiment—has a rather complicated history (Heck, don't they all!!).
The regiment can be traced back to four companies of Arkansas State Troops from Benton, Franklin and Yell counties, which marched to Bentonville in July 1861 to be assigned to a regiment of Arkansas State Troops. Instead, they were intercepted by Brig. Gen. Ben McCulloch, commanding Confederate forces in northwest Arkansas, organized into a battalion under command of Lieut. Col. Dandridge McRae, and mustered directly into the service of the Confederate States on July 15, 1861. McCulloch intended to increase the battalion to a regiment. He already had two Arkansas regiments enrolled in Confederate service—the 1st and 2nd Arkansas Mounted Rifles—and McRae’s outfit was to form the basis for a 3rd Arkansas Regiment (as if we needed another 3rd Arkansas!) so it was christened as the 3rd Battalion Arkansas Infantry. It was joined later by McNair’s regiment, which McCulloch mustered into Confederate service as the 4th Regiment Arkansas Infantry, again by-passing the State Military Board, which had already assigned that designation to Col. James D. Walker’s regiment of Arkansas State Troops. At any rate, McCulloch’s command packed up and moved north toward Wilson’s Creek, and McRae’s outfit remained for the time being as a four-company battalion.
By November 1861, four new companies from Benton, Pope and Washington counties had joined the 3rd Arkansas Battalion, making a total of eight, so McCulloch asked the War Department to authorize the battalion to be designated as a regiment, promising that the last two companies would shortly be added. McCulloch’s designation of McRae’s command as the 3rd Arkansas Regiment was rejected, since Col. Albert Rust’s command in Virginia had already been given that designation; so the War Department assigned the designation of 21st Arkansas Regiment to McRae’s command (which resulted in two 21st Arkansas Regiments—but, hey, we’re talking Arkansas here!). The new 21st Arkansas Regiment was officially established on December 3, 1861, at Camp Benjamin, Arkansas.
After the battle of Pea Ridge, the 21st Arkansas and the rest of the Army of the West was ordered to Mississippi, and went into camp at Corinth, where, on May 8, 1862, the regiment was reorganized for the war, and Lieut. Col. James H. Hobbs succeeded McRae as colonel. On May 12, 1862, while still at Corinth, the last two companies (Cos. I and K) were added to the regiment, bringing it up the required ten companies. These new companies had originally been Cos. A and B, respectively, of Williamson’s Battalion Arkansas Infantry, recently disbanded. On August 22, 1862, Lieut. Col. Squire Boone succeeded Hobbs as colonel.
Sometime after October 1862, for reasons I have been unable to determine, the 21st Arkansas was redesignated as the 15th Arkansas—this was a War Department decision, the same War Department that already saddled us with two other 15th Arkansas regiments—and I have no earthly idea why the redesignation was ordered. The War Department apparently realized it had a problem, because in February 1863 the regiment was ordered to insert the word “Northwest” in its regimental designation to distinguish it from, primarily, Col. Benjamin W. Johnson's 15th Arkansas, operating in the same general theater—thus, the 15th (Northwest) Arkansas Regiment.
As you can imagine, having three active-duty regiments, all officially designated as the 15th Arkanas Regiment, in service simultaneously makes Civil War research very invigorating. Actually, there was a fourth 15th Regiment—the 15th Regiment Arkansas Militia—but this outfit played no role in the war, only mustering once for a few days in early 1862 for its annual inspection and drill.
Unless everyone’s bored to tears by now with these posts, there are still a few more situations to talk about—the two 14th Arkansas Regiments, the two 17th Arkansas Regiments, the two 21st Arkansas Regiments, and the two 22nd Arkansas Regiments.