I don't believe that a men from Poland can talking about trench war - I suggest to read more about this theme.
We fight our part of tranch war in army of Germany, Austro-Hungarian Empire and Russia our "beloved" occupying nations. Our high command in war of 39' assumed that they will stop germans, stabilize frontline with series of field fortifications and wait for France
and Great Britain offensive. And I read many books about this 39' also my grandfather was army officer in that time.
But this is no topic for this kind of discussion.