Three other people, including a Chattanooga police officer, were wounded in the shootings.
Find out what the town is talking about below:
The shootings began shortly after 10:30 a.m. at a National Guard office in a strip mall on Lee Highway. A witness there described hearing as many as 20 shots fired there before the gunman fled.
A photo posted to Facebook by a witness shows the door of the office littered with bullet holes.
The shooter then drove 7 miles to the Chattanooga naval reserve center, where a witness told CNN she saw a man with "a high-powered rifle" fire multiple shots from a convertible silver Mustang into recruiting offices at the center shortly before 11 a.m. ET.
Four U.S. Marines were killed at the naval center, Pentagon officials told CNN. Their names have yet to be released.
The gunman, who has yet to be publicly identified, was killed at the scene. But multiple news outlets identified the suspected shooter as 24-year-old Muhammad Youssef Abdulazeez.
"This individual brutally and brazenly attacked members of our armed forces,"
Chattanooga Police Chief Fred Fletcher said at the news conference. He declined to speculate on a motive.
Because the shootings occurred at U.S. military facilities, the FBI is leading the investigation.
U.S. District Attorney William C. Killian said officials were treating the shootings "as an act of domestic terrorism."
But Ed Reinhold, special agent in charge of the FBI's Knoxville field office, said at this point there is no evidence to suggest it was.
"Sounded like it was 30, 40 shots to me,"