How were soldiers with repeating rifles deployed on the battlefield, and how were they expected to fight? I know that soldiers were trained to operate as single, cohesive units, which meant they primarily fought elbow-to-elbow in tightly closed formations. Given the widespread use of Napoleonic tactics during the Civil War, how did repeating rifles affect the structure and tactics of infantry units during that time?
Most all of the breech-loaders bought by the US Ordnance Dept. were given to cavalry units. There was no way they could have equipped millions of infantrymen with them, even if they had wanted to replace the millions of rifled muskets already in their hands. Because it is very awkward to load a muzzle-loading gun on horseback, cavalry was equipped with breech-loaders first. But the state militia units were under no such limitations, buying their own arms, and so some militia infantry had Henry rifles.
The Ordnance Dept bought very few Henry rifles: only 1,731 during the War. When assessed, in 1861, they were judged to be expensive and heavy. They also required special metallic cartridges, and the Dept. was already concerned about how it could supply the diverse ammunition for all the various breech-loaders it had already started to buy, the Sharps, Spencer, Burnside, Smith etc. But because of the state militia units equipped with Henry rifles, the War Dept. ended up buying about 4,000,000 cartridges for them anyway.
There does not seem to have been any great change in tactics in employing troops equipped with repeaters or breech-loaders. But their greater rate of fire certainly had an effect- as the War Dept itself would note, one solder that had the greater rate of fire of a breech-loader could equal a few equipped with muskets. One good example would be at the Battle of Franklin. Confederate Gen. John Bell Hood was already over-fond of frontal assaults against strong positions , but at Franklin his troops were badly mauled. The Confederate break-through around the Carter house on the first day of fighting was in part stopped by the 12th Kentucky and 65th Illinois militia units armed with Henry rifles.