The Civil War marked a turning point in the way battles were fought. Deadly new firearms-when they could be obtained-forced the development of new combat tactics among infantry and artillery, while the traditional cavalry charge was consigned to history.
In 1775 Americans went to war with smoothbore flintlock muskets and 6pounder smoothbore cannon. They fought with linear tactics-that is, infantry regiments stood in line and fired in volleys like a gigantic shotgun until their enemies' regiments faltered, and then charged with a fixed bayonet, or were driven from the field themselves. Artillery lined up between the regiments on the frontline to support the infantry. Cavalry guarded the flanks and then charged a fleeing foe. Essentially these tactics lasted through to the Mexican War of 1846, though there were minor changes. The artillery in that war featured one battery of horse artillery per regiment, providing maneuverable frontline fire support. There were other advances as well. In 1842, only four years before the Mexican War, the U.S. Army adopted a smoothbore musket that used a copper percussion cap instead of a flintlock. This made the weapon usable in rain, something that dampened the powder in the flintlock pan of muskets and made them unusable.
British weapons expert George Hanger wrote of British smoothbore flintlock muskets in the 18th century, “A soldier's musket, if it was not exceedingly ill-bored (as many of them are), will strike the figure of a man at 80 yards [73 m]; it may even at 100 [91 m]; but a soldier must be very unfortunate indeed who shall be wounded by a common musket at 150 yards [137 m], provided his antagonist aims at him; and as to firing at a man at 200 yards [182 m] with a common musket, you may just as well fire at the moon and have the same hopes of hitting your object. I do maintain and will prove, whenever called on, that no man was ever killed at 200 yards by a common soldier's musket, by the person who aimed at him.” The weapon Hanger described was essentially the smoothbore musket used by the U.S. Army in the Mexican War, be it percussion cap or flintlock.