Beneath the Iraqi city of Sinjar lies hundreds of feet of underground tunnels that the Islamic State, also known as ISIS, used to evade coalition airstrikes. These pathways were discovered after Kurdish forces recaptured the city in November 12, 2015. They were found filled with remnants of food, medical supplies, blankets, copies of the Koran, and bomb-making equipment. The tunnels opened into above-ground houses that enabled the militants to move through the city undetected. ISIS might be new, but its tactic is as old as war itself, used during the civil war and World War I, for example, as a surprise maneuver for blowing up the ground beneath the enemy's feet. Arthur Herman writes of war tunnels in "Notes from the Underground":
They are an invisible and silent threat, unless you know what to look for and where to look...the factor of the unknown can gnaw at an antagonist’s imagination, filling an entire community with fear and adding a dimension of psychological warfare to the other challenges tunnel warfare poses.