I agree that the lines were needed due to the heavy use of single-shot muskets during the US Civil War. However, these weapons were only used because the two sides refused to accept technological advances of the time. The Henry Repeating Rifle was available in 1860, but was not used by the Union until 1862, and even then in only small numbers. The Gatling Gun was also available at the time, and the only thing that kept the US Civil War from being the first 'machinegun' war was the refusal of the North to adapt to the new technology. One General (Burnside I believe) even bought 12 of the things out of his own pocket because he saw the value in them, even if the government did not.
Civil War battle lines were just as obsolete a tactic as trench warfare & "going over the top" was in WWI. Just because you ignore the technology that could have solved the problem for you doesn't mean your methods aren't obsolete. If the US military destroyed all of its equipment and went back to single-shot rifles and Civil War lines, would they be using obsolete tactics?
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