India has activated a miniature atomic reactor on board an indigenously designed nuclear submarine, the INS Arihant, which is said to be a major step towards operational deployment of the submarine and realizing a triad nuclear assault capability by the country. Official sources told local media on Saturday that the nuclear reactor on Arihant has attained \"criticality\" Friday night and the submarine was on its own power now, according to Indo-Asian News Service. Indian Prime Minister Manmohan Singh hailed the event as a big stride in building the nuclear submarine and nuclear armed forces. INS Arihant, the country\'s first indigenously designed nuclear submarine, has been undergoing trials at navy\'s submarine base in Visakhapatnam, Andhra Pradesh, southern India. However, it will take some time before the submarine can be officially launched after numerous testings. India has rented a Russian nuclear submarine in the past in its navy service.