>>64079701thats the civilian equivilent
the reality is it is because shirts got shorter and people didn't have pants as we understand them
people wore 'shifts' that came down to about mid-thigh or the knees, they wore as underwear a sort of loose boxer called 'brae' and hose rather than pants were tied to its draw string
this left a bit of a gap as shifts started to shorter
so the cod piece filled the gap
eventually someone figured out to combine it with those and thus we got pants