US Coast Guard commanders are defending the agency's proposal to periodically close 2500 square miles of the Great Lakes for machine-gun firing exercises.
The Detroit regional commander says the plan to create 34 weapons-practice zones is vital to the guard's ability to protect America's security.
US and Canadian mayors, business leaders and environmentalists have criticized the plan.
The Coast Guard says it has years of experience safely conducting live-fire training in the nation's coastal waters.
Each zone would be closed to marine traffic for about four hours, four to eight times a year.
The guard plans seven public hearings around the region, starting Monday.