Fact1: top command dispatches S21 under command of Capt. Ranvijay Singh for surveillance, Fact2: Indian Navy has been sent to sink sole Indian air-craft carrier, Fact3: Singh orders ship 's XO to conduct drill and Ghazi, Fact4: crew to head at full speed orders, Fact5: Ghazi last moment that is headed into mines
Output: The Indian Navy decodes a secret code sent from Pakistan to thenEast Pakistan modernday Bangladesh and intelligence report of a Pakistan Navys submarine called PNS Ghazi, a much more advanced submarine than S21 or any other Indian submarine, being sent through the Bay of Bengal under the command of Cdr. Razak Khan Rahul Singh. The top command dispatches S21, a submarine, under the command of Capt. Ranvijay Singh Kay Kay Menon for surveillance. To temper Singhs belligerent tendencies, the Indian Navy Admiral assigns Lt. Commander Arjun Varma Rana Daggubati, with orders to ensure that Singh does not confront any Pakistani warships and trigger a war. Ghazi blasts a merchant ship to divert attention of the Indian Navy, that has been sent to sink the sole Indian aircraft carrier, INS Vikrant. Arjun saves a girl child and a woman Taapsee Pannu, who are Bangladeshi refugees. During surveillance, S21 acquires a sonar signal of Ghazi. Singh believes that they should track down Ghazi and attack, while Arjun obstructs. Singh then orders the ships XO, Santosh Devraj Atul Kulkarni to conduct a drill and target Ghazi while doing so. They miss their target narrowly and in the process alert Ghazi of their presence. Razak, orders his crew to head towards Visakhapatnam Port at full speed and to set up mines enroute so that S21 is destroyed in their pursuit. S21 pursues Ghazis path and realizes at the last moment that it is headed into mines. It tries to change its course but a mine explodes and damages most of the batteries, propellers and circuits and the compartment with the front torpedoes gets flooded. Singh dies while trying to save Arjun as S21 sinks to the seabed. Meanwhile, Arjun, who by now is in charge of the mission, regroup and work towards reviving S21. The crew notices that the ship is incapable of moving in any direction, except up or down. Since they cannot chase Ghazi, the crew artificially triggers a one of the naval mines in its vicinity to make Ghazi return. Razak, sensing that Ghazi could be walking into a trap, diverts the ships path and starts attacking S21. Six torpedoes fired by Ghazi are avoided by S21 through depth changing maneuvers. S21 dives to 350m so that it is no longer within Ghazis sonar range despite being designed for a maximum of 250m depth. With very limited battery support, Arjun instigates Ghazi into attacking by transmitting his crew singing Saare Jahaan se Achchha and the Indian National Anthem. Riled up by S21s defiance, Razak orders another torpedo attack on S21, for which Ghazi will have to turn by 180 degrees. Arjun, dives into the flooded compartment to manually trigger the torpedoes and successfully triggers a torpedo. Ghazi also launches its torpedo at the same time. The Ghazi torpedo misses S21 narrowly, but it is hit by an S21 torpedo and disintegrates in water. Arjun is later saved alive from the flooded compartment.