In November 1971,
India and
Pakistan are on the verge of declaring war on each other as a result of the
refugee crisis precipitated by the
Pakistan Army under
Operation Searchlight. The
Indian Navy and
RAW decipher a secret code sent from
Pakistan to
East Pakistan (modern-day
Bangladesh), relating to a possible attack on an Indian naval vessel. The Navy deduces that the target may be
INS Vikrant, India's sole aircraft carrier. The top command dispatches the submarine
S21, under the command of
Captain Ran Vijay Singh, for reconnaissance missions. To temper Singh's belligerent tendencies, the Indian Navy Admiral assigns
Lt.Cmdr Arjun Varma to
S21, with orders to ensure that Singh does not confront any Pakistani warships and trigger a war. The Navy's top command soon learns that the
Pakistan Navy has dispatched
PNS Ghazi, under Cmdr. Razak Khan, to the
Bay of Bengal to confront
Vikrant. Meanwhile, to divert the attention of the enemy,
Ghazi torpedoes an Indian merchant ship. The attack is picked by
S21, which races to the scene. Noticing survivors in the wreckage, Arjun jumps into the sea and manages to rescue a girl child and a woman, both of whom are
Bengali refugees. During surveillance,
S21 acquires a sonar signal of
Ghazi. Singh believes that they should track down
Ghazi and attack, while Arjun obstructs, reiterating his instructions. Singh then orders the ship's
EXO, Lt. Commander Santosh Devraj, to conduct a drill and target
Ghazi while doing so, despite Arjun's protests. They fire a
torpedo, which misses
Ghazi narrowly, thus alerting them of their presence. Aware of the enemy's presence, Razak orders his crew to head towards
Visakhapatnam Port at full speed and to set up
mines en route, planning to destroy
S21.
S21 pursues ''Ghazi's'' path, but they realize at the last moment that it is headed into mines. Singh and Arjun frantically attempt to change its course, but a mine explodes in the stern and damages most of the submarine's batteries, propellers, and circuits. The sub blows open many leaks, with the forward torpedo compartment flooded, crippling the sub and barring it from firing its forward torpedoes. Singh dies while trying to save Arjun, as
S21 sinks to the seabed. Arjun, now in command of the sub, regroups and works towards reviving
S21. They manage to clog the sub's leaks and pump the excess water out before holding a final farewell for Singh. The crew notices that the vessel is incapable of moving in any direction except upwards or downwards. Since they are unable to chase
Ghazi, the crew artificially triggers one of the naval mines in its vicinity to lure
Ghazi to their position. Razak, believing
S21 is still operational, orders his crew to turn around to sink
S21. Arjun and Devraj plan to lure
Ghazi within its range of firing, but a suspicious Razak orders
Ghazi's course to be changed at the last minute.
Ghazi, now having the ability to attack
S21, fires six torpedoes, all of which are avoided by
S21 through depth-changing maneuvers, much to Razak's frustration. S21 dives to 350m in order to slip from
Ghazi's sonar range despite being designed for a maximum depth of 250m. With very limited battery support, Arjun provokes Razak 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 (all the way around, so that the other side faces S21
). Arjun dives into the flooded forward compartment to manually trigger the torpedoes, successfully managing to do so. Ghazi
also launches its torpedo at the same time. The torpedo launched by Ghazi
misses S21
narrowly, but it is hit by S21'
s torpedo and disintegrates in the water, killing the entire crew. S21
surfaces, and the crew manages to save Arjun from the flooded compartment in the nick of time. S21'' is later saved by a patrolling Indian Navy vessel. The ending titles narrate the mysterious circumstances of ''Ghazi's
fate, with its sinking credited to the actions of INS Rajput. It also mentions that in the aftermath of Ghazi's'' sinking,
India and Pakistan had declared war on each other, which would ultimately result in India's victory, Pakistan's surrender, and the creation of
Bangladesh. == Cast ==