File (formation)
From Wikipedia, the free encyclopedia
A file is a military term for a number of troops drawn up in line ahead, i.e. one behind the other in a column. The number of files is the measure of the width of a column of troops in several ranks one behind the other.[1][2][3][4]

Usage
Files are useful when troops don't know where the enemy is, since there are overlapping fields of fire from each soldier, and cover from a possible flanking attack. Files are at a disadvantage when there are heavy weapons nearby, supported by infantry, especially machine guns and tanks.[1][2]
Ancient Greek use
A file of men in the Greek phalanx was called a lochos (Greek: λόχος) and usually ranged from eight to sixteen men.[5]
References
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