[mcguire]

Yes and no. The problem is that in WWI, the fronts were miles deep. There were several connected trench lines backed by guarded supply, artillery, and HQ positions along with the reserves. Those breakthroughs that did happen (which never actually included cavalry, IIRC) tended to bog down, giving the enemy time to bring up reserves and counterattack.

Cavalry and machine guns don't really mix.