Tanks fire across training grounds in northern Michigan as thousands of service members practice for a battlefield military leaders say is changing rapidly. Northern Strike began in 2012 and is held twice a year. David Kennedy, a public affairs officer with the Michigan National Guard, said this summer’s exercise is the largest since it began. Gen. Ravindra Wagh of the Michigan National Guard said lessons emerging from conflicts around the world are shaping how troops train. Northern Michigan gives troops access to more than 200,000 acres of land, the Great Lakes and air, space and cyber capabilities.