Army Gen. Frank Grass, chief of the National Guard Bureau, fires an M777 155 mm howitzer during Northern Strike 2015 at Camp Grayling, Mich., July 26, 2015. Army Gen. Frank Grass, chief of the National Guard Bureau, fires an M777 155 mm howitzer during Northern Strike 2015 at Camp Grayling, Mich., July 26, 2015. SHARE: Download: Full Size (2.039974 MB) Tags: Photo Essays Credit: VIRIN: 771191-P-BCK44-089.jpg Photo Gallery