The "other" 18th Arkansas Regiment (Marmaduke's) had an Irish company. Capt. John H. Crump's Co. D, the "Shamrock Guards", was recruited among Irish riverboat men and dockworkers at Vicksburg, Mississippi. The company was organized at Vicksburg on June 18, 1861.

Marmaduke's 18th Arkansas was redesignated as the 3rd Confederate Infantry about January 31, 1862.