After the beginning of hostilities on 3 December 1971, Indian Naval radio detection equipment identified a submarine lurking about south-west of Diu harbour. The 14th Frigate Squadron of the Western Fleet was dispatched to destroy the submarine. It normally consisted five ships Khukri,, Kalveti, Krishna and Kuthar, but at the time of the incidentKuthars boiler room was being repaired in Bombay. One reason that may have prompted the decision to deploy two obsolete Blackwood-class frigates against a modern Daphne-class submarine was that the Indian Navy lacked sufficient numbers of anti-submarine aircraft. In the early hours of 9 December, Hangor picked up two sonar contacts in the area. The sonar and radar transmissions identified them as warships but Hangor failed to intercept them and lost contact when the range increased. The submarine sighted the squadron on the evening of 9 December. Khukri was still not aware of the submarine's presence and continued slowly on a steady course because she was testing an improved version of the 170/174 sonar, which required a slow speed to increase detection, despite the fact that moving on slow speed was against Indian anti-submarine doctrine. At 19:57 Hangor fired a homing torpedo on a sonar approach at Kirpan. The torpedo failed to explode and was detected by Kirpan which turned away and fired anti-submarine mortars. Khukri increased its speed and turned towards the submarine, which then fired a second torpedo directed at Khukri. The torpedo struck Khukri and exploded under its oil tanks. According to the Pakistani submarine captain, Commander Ahmed Tasnim, the ship sank within two minutes. Other sources claim that Khukri was struck by three torpedoes before going down. After a few minutes, Kirpan turned back to attack Hangor with depth charges, as her anti-submarine mortars had broken down. Hangor then fired another torpedo at Kirpan before turning away. Hangor patrolled the region for the next four days before returning safely to her berth.
Casualties
To date, Khukri is the only ship lost in combat in the history of the Indian Navy. 18 officers and 176 sailors were lost in the sinking. The captain, Mahendra Nath Mulla, was among the casulties. He has remained so far the only Indian captain to go down with a vessel. He was posthumously awarded India's second-highest military honour, the Maha Vir Chakra. There is a memorial to the dead sailors in Diu. The memorial consists of a scale model of Khukri encased in a glass house, placed atop a hillock facing the sea. The memorial was inaugurated by Vice Admiral Madhvendra Singh as the flag officer commanding-in-chief.
Controversy
Responsibility for errors by Indian naval officers related to the sinking has caused some controversy. The naval officer who led the inquiry into the sinking, Benoy Bhushan, has claimed that India's official naval history invented fictional accounts to cover up bungling and a surviving sailor from the frigate, Chanchal Singh Gill, has called for an investigation and withdrawal of gallantry awards to negligent officers in the squadron.
