This is coolbert:
The tunnels of Gaza:
"Hamas' Massive Network Of Underground Tunnels Is A Military Game-Changer"
"July 25, 2014 - - A network of tunnels Palestinian militants have dug from Gaza to Israel — dubbed "lower Gaza" by the Israeli military — is taking center stage in the latest war between Hamas and Israel."
"Gaza's Hamas rulers view them as a military game changer in its conflict with Israel. The Israeli military says the tunnels pose a serious threat and that destroying the sophisticated underground network is a key objective of its invasion of Gaza."
"Israel has known about the tunnels for several years, but has been hard-pressed to find an effective way to block them. Now it is counting on its ground war to at least reduce the threat."
Those tunnels are force multiplier for the asymmetric fighter. You make the enemy fight on your terms and not the other way around. Tunnels allowing for sanctuary and also as fighting positions from which offensive action can be initiated.