The National Defence Academy (NDA) is a joint services academy of the Indian Armed Forces. It provides pre-commission training to cadets of the Indian Army, Indian Navy, and Indian Air Force. Candidates are selected through a written exam conducted by the Union Public Service Commission twice a year, followed by interviews covering general aptitude, psychological tests, and medical tests. Eligible candidates must be Indian citizens between 17-21 years old and have completed 12th standard education. The exam tests candidates on mathematics, general ability, intelligence and personality. Qualifying candidates are then called for further testing at the Services Selection Board.