Director: Sankalp Reddy
Writer: Sankalp Reddy
Cast: Rana Daggubati as Lieutenant Commander Arjun Varma
Kay Kay Menon as Captain Ranvijay singh
Atul Kulkarni as Lieutenant Commander Santosh Devraj, Executive Officer,
Taapsee Pannu as Dr. Ananya, a Bengali doctor turned refugee
Om Puri as Admiral V.S. Nanda, Indian Navy
Nassar as Vice Admiral K.T. Raman, Indian Navy
Milind Gunaji as Girish Kumar, RAW Agent
Rahul Singh as Commander Zafar Mohammad
Satyadev Kancharana as Rajeev Thakur, Sonar operator S21
Ravi Varma as Kamalakar Shinde, Battery operator of the S21
Priyadarshi Pullikonda as Lt.Nilesh Mishra, Radio operator of the S21
Bharath Reddy as B.Sanjay of the S21
Bikramjeet Kanwarpal as Pakistan Navy Staff Officer
Thiruveer as V.Murthy, Depth Controller of the S21
Jay Jha as Navigation Officer, Ghazi
Capt SN Ahmed as Lieutenant Taan Singh, torpedo operator of the S21
Niteesh Pandey as N.Tiwari, steering controller of the S21
Kunal Kaushik as Kapil Singh
Malyaban Lahiri as Ranjan Sengupta, Junior Officer of the S21
Naren Yadav as Ram Sagar of the S21
Ramanuj Dubey as Indian cook Iqbal S21
Ravi Kumar Shada
Akshay Mittal as Sublieutenant – Indian Naval Navigation Officer S21
Rama Rao Jadhav as Pump Controller S21
Appaji Ambarisha Darbha as Ananya’s father
The Indian Navy decodes a secret code sent from Pakistan to then-East Pakistan (modern-day Bangladesh) and intelligence report of a Pakistan Navy’s submarine called PNS Ghazi to attack INS Vikrant much more advanced 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 Singh’s 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 air-craft 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 ship’s EXO, Lt. Commander 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 en-route so that S21 is destroyed in their pursuit.
S21 pursues Ghazi’s 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 sea-bed.
Meanwhile, Arjun, who by now is in charge of the mission, regroups 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 one of the naval mines in its vicinity to make Ghazi return. Razak, sensing that Ghazi could be walking into a trap, diverts the ship’s path and starts attacking S21.
Six torpedoes fired by Ghazi are avoided by S21 through depth changing maneuvers. S21 dives to 350 m so that it is no longer within Ghazi’s sonar range despite being designed for a maximum of 250 m 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 S21’s defiance, Razak orders another torpedo attack on S21, for which Ghazi will have to turn by port 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.