By Simon Kent.
Kurdish Peshmerga forces in newly liberated Sinjar, the Yazidi majority town en route to Mosul, have discovered an ISIS tunnel complex of fighting positions.
The Wall Street Journal has documented the find in a photo essay report.
Tunnel complexes have previously been used by ISIS in the battle of Jurf al Sakhar last year, as well as more recently in Fallujah.
Tunnel warfare proved lethal against Americans in Vietnam, giving the enemy the advantage of concealed movement and surprise attacks. It is a common tactic when defenders are outnumbered, but vulnerable to powerful aerial bombardment.
The find demonstrates the determination of ISIS to hold onto captured terrain, and could be a grim warning how urban battles in Mosul, Ramadi and Fallujah could pan out.
(Source: The Wall Street Journal)