The following article may shed some light on this topic (italics mine):
"In Civil War tactics, the principal combat arm was infantry. Its most common deployment was a long "line of battle," 2 ranks deep. More massed was the "column," varying from 1 to 10 or more companies wide and from 8 to 20 or more ranks deep. Less compact than column or line was "open-order" deployment: a strung-out, irregular single line.
Battle lines delivered the most firepower defensively and offensively. Offensive firepower alone would not ensure success. <font color="yellow"><i>Attackers had to charge, and massed columns, with their greater depth, were often preferable to battle lines for making frontal assaults. Better yet were flank attacks, to "roll up" thin battle lines lengthwise.</i></font id="yellow">Offensive tacticians sought opportunity for such effective flank attacks; defensive tacticians countered by "refusing" these flanks on impassable barriers. In either posture, tacticians attempted to coordinate all their troops to deliver maximum force and firepower and to avoid being beaten "in detail" (piecemeal). Throughout, they relied on open-order deployment to cover their front and flanks with skirmishers, who developed the enemy position and screened their own troops.
Open order, moreover, was best suited for moving through the wooded countryside of America. That wooded terrain, so different from Europe's open fields, for which tactical doctrine was aimed, also affected tactical control".
Source: "Historical Times Encyclopedia of the Civil War" Editor, Patricia L. Faust
Lt. Tom Bridges
3/2/XIX/AoS
Kansas Dragoons
