That far exceeds the 295 American combat deaths in Afghanistan in 2012 and compares with 301 military suicides in 2011.
Some private experts predict that the trend will worsen this year.
Defense Secretary Leon Panetta and others have called military suicides an epidemic.
The Army had the highest number of suicides among active-duty troops last year at 182, but the Marine Corps had the largest percentage increase – up 50 percent to 48.
The Air Force recorded 59 suicides and the Navy had 60.