Army Reserves serving when needed

Being in the Army Reserve allows you to pursue your civilian career or college education while you serve your community. You will spend one weekend a month in training and two weeks a year attending a Field Training Exercise (FTX). Soldiers in the Army Reserve may be called to Active Duty to provide their expertise. Your service in the Army Reserve may range from three to six years, depending on your Army Reserve job.

 http://www.goarmy.com/about/service-options/army-reserve.html