The scale and intensity of the American Civil War is difficult to comprehend today. The number of soldiers killed on both sides is estimated to be around 620,000—more than the Unites States’ losses in all other wars combined. Even this numbing statistic, however, fails to convey the particularly grim spectacle of a Civil War battle, in which opposing ranks of closely packed soldiers fired volley after volley into each other at virtually point-blank range.

The dense, linear formations in which both Union and Confederate armies fought may baffle us today, but at the time they were the conventional military wisdom, founded on centuries of experience about how battles were fought and wars were won. Having soldiers stand and fight shoulder to shoulder helped ensure discipline in the face of enemy fire. Even more importantly in the heat and confusion of battle, close formations facilitated command, control, and maneuver through voice and drum commands.

The weapons traditionally carried by soldiers in these formations also informed their tactics, and vice versa. Since the 17th century, the typical European and American soldier had been armed with a smooth-bore musket—essentially a muzzle-loaded steel tube which fired a large lead ball. It was only accurate to about 50 yards , but when used by one massive formation against another, even an inaccurate shot would likely hit an enemy soldier, if not the one targeted.

By the Civil War, improvements had been made in musket technology that allowed a new type of conical bullet to be fired from a “rifled”—or spirally grooved—barrel. This imparted a spin to the bullet that increased its accurate range to approximately 300 yards. Opposing armies equipped with rifled muskets could now engage each other at much extended ranges, effectively multiplying the lethality of each individual soldier, and rendering conventional linear tactics almost suicidal. The rifled musket had transformed the traditional battlefield before the first shot of the Civil War was even fired. Unfortunately, neither side fully recognized it.

Militaries tend to be conservative, cautious organizations, hewing carefully to lessons learned in previous conflicts—often with disastrous results. Such was the case with both Union and Confederate generals in the Civil War. Facing the challenges of transforming hundreds of thousands of untrained volunteers and conscripts into soldiers, they stuck to old, tested—and obsolete—tactics. Largely as a result, the vast citizen armies they equipped with the new rifled musket would slaughter each other with unprecedented efficiency.

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