The 18th Arkansas Infantry Regiment or the 3rd Confederate Infantry Regiment (also known as "Marmaduke's regiment") was an infantry formation of the Confederate States Army in the Western Theater of the American Civil War.

The unit was also briefly identified as the 1st Arkansas Infantry Battalion. The unit was most often referred to as the 3rd Confederate Infantry Regiment. The designation "Confederate Infantry Regiment" was intended to convey the difference between Provisional Confederate Army units and Regular Confederate Army Units, with Provisional units being those regiments who received a state designation such as "XX Arkansas Infantry Regiment". In practice, the designation was most often utilized when Regiments were assembled utilizing companies from more than one Confederate state. The "3rd Confederate Infantry Regiment" is occasionally misidentified as the 3rd Arkansas Infantry Regiment commanded by Colonel Van H. Manning.

Formation The 18th Arkansas Infantry started out as 7 of 22 companies which comprised the so-called "Hindman Legion." Col. Thomas C. Hindman had recruited ten companies at his own expense for the 2nd Arkansas Infantry Regiment, and then an additional seven companies at his own expense which, along with four cavalry companies and an artillery battery, became known as the Hindman Legion. The "Legion" was not approved as an organization, and, after being mustered into the Confederate service on July 27, 1861, reverted to a regiment (the 2nd Arkansas Infantry Regiment), an infantry battalion (the 1st Arkansas Infantry Battalion) and a cavalry battalion (the 6th Arkansas Cavalry Battalion). Capt. John S. Marmaduke was assigned as commander of the 1st Arkansas Infantry Battalion and promoted to lieutenant-colonel on August 1, 1861.

A company from the 15th Tennessee Infantry Regiment was transferred to the 1st Arkansas Battalion, and two additional companies were added on December 18, 1861, which brought the battalion up to ten companies. On January 1, 1862, the unit was formally designated as a regiment, the 18th Arkansas Infantry, and Marmaduke was promoted to colonel. On January 31, 1862, the regiment was redesignated as the 3rd Confederate Infantry because it contained units from multiple states.Howerton, Bryan R. "Re: Understanding the 3rd Confederate", Arkansas in the Civil War Message Board, Posted 29 July 2009, Accessed 14 February 2012, http://history-sites.com/cgi-bin/bbs53x/arcwmb/webbbs_config.pl?noframes;read=20597

The 3rd Confederate Infantry was composed of the following companies:

Company A – the "Little Rock Grays" – of Pulaski County, Arkansas, commanded by Captain James B. Johnson. This company was originally Company L, 1st Arkansas Infantry Battalion. Company B – the "Young Guard" – of Shelby County, Tennessee, commanded by Captain John F. Cameron. Company C – the "Fletcher Rifles" – of Mississippi County, Arkansas, commanded by Captain Elliot H. Fletcher Sr., This company was originally Company O, 1st Arkansas Infantry Battalion. Company D – the "Shamrock Guards" – of Warren County, Mississippi, commanded by Captain John H. Crump. This company was originally Company P, 1st Arkansas Infantry Battalion. Company E – the "Linden Dead-Shots" – of St. Francis County, Arkansas, commanded by Captain Poindexter Dunn. This company was originally organized as a volunteer militia company in the 19th Regiment, Arkansas State Militia, from St. Francis County, with militia commissions being issued to its officers on May 16, 1861.Arkansas Military Department Records, List of Commissioned Officers in State Militia 1827–1862, Microfilm Roll 00000038-8, Page 280 The company was assigned as Company Q, 1st Arkansas Infantry Battalion. This company was originally organized as a volunteer company in the 19th Regiment, Arkansas State Militia on May 16, 1861. Company F – the "Chalk Bluff Rebels" – of Greene County, Arkansas, commanded by Captain William Reed. This company was originally Company R, 1st Arkansas Infantry Battalion. Company G – the "Pine Bluff Artillery" – of Jefferson County, Arkansas, commanded by Captain Fredrick P. Steck. This company was originally Company S, 1st Arkansas Infantry Battalion. This company was originally organized as a volunteer artillery company in the 34th Regiment, Arkansas State Militia on April 21, 1861.Arkansas Military Department Records, Spanish American War, List of Commissioned Officers of the Militia 1827–1862, Arkansas History Commission, Microfilm Roll 38- Company H – the "Swamp Rangers" – of Warren County, Mississippi, commanded by Captain H. V. Keep. This company was originally Company T, 1st Arkansas Infantry Battalion. The company was consolidated with Company E on January 22, 1862. Company I – the "Burrowville Mountain Guards" – of Searcy County, Arkansas, commanded by Captain John J. Dawson. This company was originally Company(?), 1st Arkansas Infantry Battalion. The company was consolidated with Company A on April 23, 1862. Company K – the "Rector Guards" – of Searcy County, Arkansas, commanded by Captain Ira G. Robertson.

Note: Companies I and K were composed primarily of suspected members of the so-called Arkansas Peace Society, who were arrested and sent to Little Rock by members of the 45th Arkansas Militia Regiment, where they were given the choice of Confederate service or imprisonment. Most of the men were from Searcy County. The officers were non-Peace Society men appointed by the Governor.Howerton, Bryan R. "Re: Understanding the 3rd Confederate", Arkansas in the Civil War Message Board, Posted 29 July 2009, Accessed 14 February 2011, http://history-sites.com/cgi-bin/bbs53x/arcwmb/webbbs_config.pl?noframes;read=20600

Service Assigned to Hindman's Brigade, Hardee's Division in the Army of Central Kentucky from December 1861 through January 1862.United States. War Dept. The War of the Rebellion: A Compilation of the Official Records of the Union And Confederate Armies. Series 1, Volume 7., Book, 1882; digital images, (http://texashistory.unt.edu/ark:/67531/metapth154610/m1/858/?q=Army of Mississippi : accessed June 27, 2012), University of North Texas Libraries, The Portal to Texas History, http://texashistory.unt.edu; crediting UNT Libraries, Denton, Texas. The unit was involved in an engagement at Rowlett's Station, Kentucky, on December 17, 1861. Assigned to Hindman's (later Liddell's) brigade, Army of Mississippi in March, 1862 where it participated in the Battle of Shiloh on April 6–7, 1862 and in the Corinth Campaign from April through June of that year. At the battle of Shiloh the 3rd Confederate bore the guiding colors of Hindman's Brigade and captured the first prisoners of the day. Colonel Marmaduke was mentioned with praise in the official reports. In the second day's battle he was wounded and disabled, and while in hospital was recommended for promotion to the rank of brigadier-general. Colonel Marmaduke commanded his brigade of Arkansans during the Siege of Corinth, and later was ordered to the Department of the Trans-Mississippi.Martin, George, "Re: Understanding the 3rd Confederate", Arkansas in the Civil War Message Board, Posted 29 July 2009, Accessed 27 June 2012, http://history-sites.com/cgi-bin/bbs53x/arcwmb/webbbs_config.pl?noframes;read=20588

In early May 1862 the Confederate forces underwent an army-wide reorganization due to the passage of the Conscription Act by the Confederate Congress in April 1862. All twelve-month regiments had to re-muster and enlist for two additional years or the duration of the war; a new election of officers was ordered; and men who were exempted from service by age or other reasons under the Conscription Act were allowed to take a discharge and go home.United States. War Dept. The War of the Rebellion: A Compilation of the Official Records of the Union And Confederate Armies. Series 1, Volume 10, In Two Parts. Part 2, Correspondence, etc., Book, 1884; digital images, (http://texashistory.unt.edu/ark:/67531/metapth154614/m1/500/?q=Army of Mississippi : accessed June 17, 2012), University of North Texas Libraries, The Portal to Texas History, http://texashistory.unt.edu; crediting UNT Libraries, Denton, Texas. Officers who did not choose to stand for re-election were also offered a discharge. The reorganization was accomplished among all the Arkansas regiments in and around Corinth, Mississippi, following the Battle of Shiloh.

In the reorganization of Confederate forces before the start of the Kentucky Campaign, the 3rd Confederate, now under the command of Lieutenant Colonel Henry Virtner Keep was assigned to Brigadier General Sterling A. M. Wood's 4th Brigade of Major General Simon Bolivar Buckner's 3rd Division of Major General William Joseph Hardee's Corps of the Army of Mississippi. The regiment participated in Battle of Perryville, Kentucky, in October 1862.Holman, Kurt. "Perryville Order of Battle: Forces Present at Perryville, October 8, 1862 (Revised January 10, 2008)", unpublished paper, Perryville Battlefield State Historic Site.

In November 1862, following the Kentucky Campaign, General Bragg united his Army of Mississippi and the General Kirby Smith's Army of Kentucky to create the Army of Tennessee. In the reorganization, Wood's Brigade, including the 3rd Confederate now under the command of Major John F. Cameron, was assigned to Cleburne's Division and fought in the Battle of Stones River.Official Records, Series I, Volume XX, Part 1, pages 658-661 Major J. F. Cameron filed the after action report of the 3rd Confederate Infantry following the battle of Stone's River (Murfreesboro):Official Records PAGE 906-29 KY., MID. AND E. TENN., N. ALA., AND SW. VA. [CHAP. XXXII. [Series I. Vol. 20. Part I, Reports. Serial No. 29.]

By the time of the Battle of Chickamauga, the 3rd Confederate had been field consolidated with the 5th Confederate Infantry due to battle losses and placed under the command of Colonel James A. Smith. The consolidated 3rd/5th Confederate Infantry was assigned to the brigade of Brigadier General Lucius E. Polk in Cleburn's Division of the Army of Tennessee.United States. War Dept. The War of the Rebellion: A Compilation of the Official Records of the Union And Confederate Armies. Series 1, Volume 30, In Four Parts. Part 1, Reports., Book, 1890; digital images, (http://texashistory.unt.edu/ark:/67531/metapth152978/m1/241/?q=Arkansas : accessed June 27, 2012), University of North Texas Libraries, The Portal to Texas History, http://texashistory.unt.edu; crediting UNT Libraries, Denton, Texas.

When General Joseph E. Johnston assumed command of the Army of Tennessee to oppose General Sherman's Atlanta campaign, the 3rd Confederate was assigned to Govan's Brigade. The 3rd Confederate participated in the battles of Dalton, Resaca, New Hope Church, Kennesaw Mountain, Atlanta, and the Siege of Atlanta. During the Battle of Atlanta on July 22, 1864, the 3rd Confederate had only 62 effectives and reported 9 casualties.United States. War Dept. The War of the Rebellion: A Compilation of the Official Records of the Union And Confederate Armies. Series 1, Volume 38, In Five Parts. Part 3, Reports., Book, 1891; digital images, (http://texashistory.unt.edu/ark:/67531/metapth154634/m1/758/?q=Arkansas : accessed June 26, 2012), University of North Texas Libraries, The Portal to Texas History, http://texashistory.unt.edu; crediting UNT Libraries, Denton, Texas.

The regiment and it colors were captured, along with much of Govan's Brigade at the Battle of Jonesboro, Georgia, on Sept. 1, 1864. Due to a special cartel between Union General Sherman and Confederate General John B. Hood, the unit was quickly paroled and exchanged for Union prisoner held at Andersonville Prison. The regiment re-entered service approximately a month later.