Acronyms that contain the term hollow square 

hollow square

An infantry square, also known as a hollow square, was a historic combat formation in which an infantry unit formed in close order, usually when it was threatened with cavalry attack. As a traditional infantry unit generally formed a line to advance, more nimble cavalry could sweep around the end of the line and attack from the undefended rear or burst through the line, with much the same effect. By arranging the unit so that there was no undefended rear, a commander could organise an effective defense against a cavalry attack. With the development of modern firearms and the demise of cavalry, that formation is now considered obsolete.

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