There are lots of such cases.

Modern war is no 'clash of tidily sorted Roman legions': the battlefield is moving that fast, that one is deploying whatever is available.

There are lots of such cases. See the counter-strike on RFA's bridgeheads: four regular Ukrainian brigades were involved - none of them entirely, but all just 'by battalions'.

Modern war is no 'clash of tidily sorted Roman legions': the battlefield is moving that fast, that one is deploying whatever is available.