Oct. 1, 2006 - A Close-In Weapon System (CIWS) fires during a Pre-Aim Calibration (PAC) fire aboard the amphibious assault ship USS Essex (LHD 2). CIWS is the self-defense system that combines a 20mm Gatling gun with search and tracking radar to provide surface ships with terminal defense against anti-ship missiles. Essex is the Navy’s only forward deployed amphibious assault ship and is the flagship for the Essex Expeditionary Strike Group out of Sasebo, Japan.