Many military feats of contemptory indian history are unknown .
Most of us do not know that the Indo pak war of 1971 was preceded by a quiet sinking of Pakistan naval submarine PNS Ghazi off Vizagapatnam .
The PNS ship had come to Indian waters to target INS Vikrant the only aircraft carrier of the Indian navy to cripple it before war was declared but Indian defence intelligence recognises this and sends S 21 an Indian submarine which is technically inferior to the Pakistani submarine .
The film is all about what happens deep under the water for 18 days .
The PNS Ghazni fires on an innocent merchant navy ship initially to divert attention .
The pak submarine when detected is fired at by S21 but missed
This exposes the Indian submarine which are hit by mines planted by PNS Ghazni
S21 sinks to bottom
Its brave captain dies and asst takes over
The submarine loses its power to chase the enemy and can only go up or down and to fire its torpadoe it loses the automatic controls and needs a manual torpadoe firing !
How cleverly S21 avoids the PNS Ghazni torpadoeing barrage by quietly adjusting its depths and later manually fires single torpadoe that sinks the Paki vessel is the film taken brilliantly .
Though Pakistan denied this ever happened and said its submarine had sunk because of an accident from its mines stock .
But it started the indo pak war immediately obviously as a revenge .
We all know how it was defeated too .
Such stories becoming film scripts is brilliant in fact they should become part of school text books .