Question

Colt revolvers and Springfield muskets were the Civil War’s most popular firearms, but the era also gave rise to some of the earliest machine guns. Of these, perhaps none is more infamous than the Gatling gun, a six-barreled piece that was capable of firing up to 350 rounds a minute. The U.S. government never ordered the Gatling in bulk, but Union General Benjamin Butler privately purchased several of the intimidating weapons in 1863 and later used them during the Petersburg Campaign.

Other rapid-fire guns included the Williams gun—a Confederate breechloader first unveiled at the Battle of Seven Pines in 1862—and the Billinghurst-Requa battery gun, which consisted of 25 rifle barrels arranged side by side. Viewed as too inefficient and unwieldy for infantry combat, these weapons were generally used for guarding bridges and other strategic locations.
short summarized

Answer 1

During the Civil War early machine guns appeared—most famously the six-barreled Gatling (up to 350 rounds/min), which the U.S. didn’t buy in bulk but General Benjamin Butler privately bought and used in 1863 during the Petersburg Campaign. Other rapid-fire weapons included the Confederate Williams breechloader (first seen at Seven Pines, 1862) and the 25-barrel Billinghurst-Requa; judged unwieldy for infantry, they were mostly used to guard bridges and strategic sites.