Authorities say the shooting happened outside a building on the property of the Naval Support Activity Mid-South at 12:47 p.m. CT. The suspect, identified as a member of the National Guard, was quickly apprehended by other National Guard members.
The gunshot victims, who were also National Guard members, were rushed to an area hospital with non-life-threatening injuries.
A source told the Associated Press that the gunman was a recruiter who had been relieved of duty. The base is a shared facility with the Tennessee National Guard.
The base was briefly put on lockdown when shots were fired. Navy and base police are working with local law enforcement in the investigation.
Millington is located about 20 miles northeast of Memphis.
ABC News and The Associated Press contributed to this report.