Yeah, I could just see them coming out of the trenches like drowned rats.
I looked at the 4 inch gun cart, but it was just over kill, too hard to move by hand. If you had enough pump to pressurize a 2 inch bore nozzle that would be something.
I have heard that some of the fire boats with an unlimited supply of water and high pressure pumps can blast through brick walls. Gotta be careful with high pressure water. Water jets with abrasive slurry can cut through very heavy sections of hardened steel.