Complex sentence: The use of these fire-arms required tactical innovations like the counter-march of files of musketeers to enable rapid volley fire by ranks; such complicated manoevres had to be instilled by constant drilling.
Split into simpler sentences: The use of these fire-arms required tactical innovations like the counter-march of files of musketeers to enable rapid volley fire by ranks. Such complicated manoevres had to be instilled by constant drilling.