The INS Chakra, the Indian Navy's nuclear attack submarine, is on the prowl 200 km off Goa's coast in the Indian Ocean, scouring the seas for the sound of "enemy submarines." One of the fastest and deepest diving submarines in the world, the Chakra, acquired on lease from Russia, has been specifically deployed to train for a new threat - Chinese nuclear submarines operating with increasing frequency in the Indian Ocean. On this occasion, the Chakra's "targets" are the Indian Navy's own submarines simulating the movements of Chinese and Pakistani submarines.