VOLK FIELD, Wisconsin - Air crews from around the country descended on Volk Field Combat Readiness Training Center for a two-week combat training exercise June 8-19.Air National Guard units from Madison, Wisconsin and Milwaukee joined others from Tulsa, Oklahoma, Duluth, Minnesota, Tucson, Arizona, and Mountain Home Air Force Base, Ohio, as well as an active duty Air Force unit from Offutt Air Force Base, Nebraska, for Northern Lightning - an annual exercise that prepares air crews for combat against a near-peer adversary.The 2015 edition of Northern Lightning featured a first for an Air National Guard exercise as it incorporated privately contracted aircraft to simulate adversaries in the skies over Wisconsin.