sentences:  This was increased further by the introduction of a titanium dioxide and wax compound known as "Swedish Additive" on for her tour in Vietnam, and later used on all four "Iowa"s when they were reactivated in the 1980s.These measures were further augmented by the addition of polyurethane jackets, which were placed over the powder bags to reduce gaseous erosion during the firing of the guns.These measures greatly prolonged barrel life, and ultimately resulted in a shift from measuring barrel life in equivalent service rounds (ESR) to measuring barrel life in fatigue equivalent rounds (FER).