Sgt. Culin's Hedge-Chopper invention significantly helped by allowing attacks across a bocage in multiple locations instead of having to wait for a bulldozer Sherman to make a path. Having limited avenues of attack is a recipe for disaster. Did it result in the Cobra breakout? Not at all, although it got them to the point of the breakout quicker and with a few less casualties. The book "Death Traps" gives July 22, 1944 as the date of the first group demonstration of the device. I'm sure it must have been tried on a few tanks before this, but after this demonstration they were assigned to put in on the tanks en masse.