Whenever I see references to US Civil War infantry it is usually in reference to the use of muzzle loaders. It's understandable since only a small amount of soldiers would use breech loading weapons in the Civil War, but it makes me wonder if US soldiers changed tactics when using/facing them.
The impression I get from the Franco-Prussian war was that breech loading rifles forced both combatants to rely much more heavily on open order formations. Meanwhile in the Austro-Prussian war Prussian infantry with breech loaders had an enormous advantage against Austrians with muzzle loaders, and many Austrian attempts at charging in closed formations failed. I wonder if a similar change occurred during the US Civil War with breechloader equipped troops.
While I don't have an exhaustive knowledge of all the tactical thinking of all the officers in the Civil War, how many of them adhered to Hardy and Casey's 1855 manuals, breech-loaders didn't seem to have had much effect on most of them. Certainly, the Ordnance Dept. itself thought only in terms of simple firepower- if a soldier with a breech-loader could fire five times as fast as one with a muzzle-loader, a troop of ten soldiers equipped with them could replace a troop of fifty. But the actual effect on the battlefield was less than in Europe: while both forces in the Franco-Prussian War were armed with breech-loading guns ( the Dreyse needle-gun and the Chassepot) in the US Civil War most of the breech-loaders were only given to cavalry: although there was a recognition that the entire army would be better off with them, when the crisis happened breech-loaders were impossible to manufacture in the huge quantity needed to equip it.
Because some militia units bought their own guns, though, there were cases where infantry equipped with breech-loaders had great effect. At the Battle of Franklin, some of John Bell Hood's army charged against some militia equipped with Henry rifles and took great casualties. But Hood's army took enormous casualties there, in general, and perhaps that's indicative of the whole war: the adoption of the Minié bullet and rifled muskets itself increased the rate of fire, range and lethality from what it had been in the 1840's, when officers like Lee, Grant and Sherman had gotten their start. The massed-charges at the battles of Fredericksburg and Cold Harbor also resulted in huge losses for the attackers- and those were against muzzle-loaders.
One officer who took advantage of the increased firepower of the cavalry was Colonel Emory Upton, who discovered dismounting his Spencer-equipped troops could have great effect ( get a man off a horse, and his aim improves...). He seems to have realized new tactics were needed: he had experienced the battle of Fredericksburg . In 1864 he. used massed columns to quickly attack a small section of the Confederate line at Spotsylvania Courthouse and break through. That attack failed from lack of support ( one of the problems the same tactic would often have during WWI) but Winfield Scott Hancock used it again and was successful. After the war's end, Upton was a very big part of a vigorous debate about the need to change the tactical thinking of the army. As the army immediately began to equip all troops with breech-loaders, it was certainly needed. Upton's talents were recognized, and he was made instructor in tactics at West Point from 1870-75.. He was also sent by William T. Sherman on a tour of Europe and , after learning about European developments, made important recommendations to the War Dept. and authored many important papers on tactics. His influence on the American army has been compared to Alfred Thayer Mahan's influence on the navy. Unfortunately, he died quite early, in 1881.
Perry D Jamieson: Crossing the Deadly Ground