The operation did not bring about the desired success. For instance, when troops found a tunnel, they would often underestimate its size. No one was usually sent in to search the tunnels, as it was so hazardous. The tunnels were often rigged with explosive booby traps or punji stick pits. The two most common responses in dealing with a tunnel opening would be to flush the entrance with gas, water or hot tar to force the Viet Cong soldiers into the open or to toss a few grenades down the hole and "crimp" off the opening. Those approaches proved ineffective because of the design of the tunnels and the strategic use of trap doors and air filtration systems.