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Rarely told story of avoidable loss of INS Khukri in 1971: A general’s honest account

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India’s 14 squadron was tasked to hunt Pakistan submarine PNS Hangor spotted near Diu. The 3-frigate squadron was one short as INS Kuthar broke down.

INS Khukri was one of the Blackwood anti-submarine frigates built by Britain in the 1950s and inducted into the Indian Navy towards the end of 1959. The Khukri, the Kirpan and the Kuthar were designated as ‘second class anti-submarine frigates’.

According to Rear Admiral Raja Menon, the Indian Navy was unhappy with the short-range sonars being given with the Blackwood class of anti-submarine frigates and requested Britain for the better medium-range sonars. The reply given, according to the Admiral, was that the better sonars were to be given only to NATO countries.

During the 1971 war these three anti-submarine frigates were pitted against Pakistan’s Daphne class submarines. These submarines were built in France in the late 1960s and were the best conventional submarines of that time. Pakistan had three of them – the Hangor, the Mangro and the Shushuk. The range of the sonars aboard the F-14 Squadron, that is, on the Khukri, Kirpan and Kuthar was approximately 2,500 m whereas the detection capability of the Daphne submarines was approximately 25,000 m, that is, ten times more.

A scale model of INS Khukri | Commons

Khukri attacks enemy submarine

From 22 November 1971, PNS Mangro a Daphne class submarine was on patrol outside Bombay harbour, lying in wait for ships of the Indian Navy. Another Pakistani submarine PNS Hangor was on patrol in the vicinity of Okha. On 1 December, Hangor received orders to replace Mangro as she had completed her tour of duty outside Bombay.

The F-14 Squadron (Indian Navy) was at sea with the Eastern Fleet when the Kuthar suffered a burst boiler and had to be moved back to Bombay. Unable to move under its own steam, Kuthar had to be towed back by INS Kirpan and both ships were escorted by INS Khukri. On their way back, the squadron was very vulnerable as it had one ship being towed, another towing and the third providing escort. En route there were many alarms of submarines. Some were no doubt false alarms and the Khukri, aware of its task to get the squadron safely back to Bombay, attacked these various threats on its own. One of these targets, the crew felt, was definitely an enemy submarine and also that the submarine suffered a hit. The entire attack, including the explosion, was recorded on tape. Aware of the responsibility to get the squadron back to Bombay, the Khukri could not wait for the signs of a hit in the form of oil slicks or flotsam and returned to Bombay on 6 December where she made a claim that she had made contact with an enemy submarine and had damaged or destroyed it but could not produce concrete proof. This particular incident occurred on 5 December 1971. The three ships reached Bombay on 6 December.

Being aware of the less than adequate performance of the existing sonars with the F-14 Squadron and some other ships, the Indian Navy had instituted a research project with the Bhabha Atomic Research Centre (BARC) to find ways and means by which the performance of existing sonars could be improved. Lieutenant VK Jain, a bright, young naval officer was working on this project at the BARC. Certain positive outcomes had emerged from the research. These research projects, however, were incomplete. Headquarters Western Naval Command decided it would be a good idea to incorporate the version of the sonar that was still in the experimental stage at BARC on the Khukri. Lieutenant VK Jain came aboard the Khukri on 6 December, the day the Khukri reached Bombay.

INS Khukri Memorial | Jasumati Patel/Twitter

Hangor gives away her location

That submarines could pick up ship’s sonars at least twice the range of the detection capability of surface ships was known not only to the Indian Navy but to all the navies of the world. However, surface ships had the advantage of much higher speed and manoeuvrability as compared to submarines.

It was about this time, that is on 5 December, that the location of the Hangor was detected by direction finders of the Indian Navy. The direction finders placed the enemy submarine approximately 16 nautical miles away from Diu. Having located an enemy submarine in Indian waters, action had to be initiated to hunt and destroy this submarine before it could damage Indian ships. The curious part of this incident is that in published material both in India and Pakistan no one examined in depth why the Hangor gave away her location by breaking well-established and accepted procedure by communicating on high frequency (HF) transmissions, as these were likely to be intercepted and her location pinpointed.

Some information, however, is available in ‘Bubbles of Water’, an anthology of short stories. The story ‘Repairing the air conditioner on patrol’ shows that the Hangor was having trouble with her air conditioner sometime around 1 December and that this was a major repair task and could only be carried out if she surfaced. The risk to do this in enemy waters was immense but the captain took the risk, surfaced, and repaired the air conditioner which, according to his estimate, would take more than a day and a half, that is, thirty-six hours. She apparently informed Karachi of her predicament and asked for orders. Her HF transmission was, however, intercepted by the Indian Navy direction finders on 5 December and that is how she was located. This happened around 5 December and not the date mentioned in the article, that is, 1 December.

If this is correct then there is a connection between the Khukri’s claim of encountering an enemy submarine and damaging it.

INS Khukri | Youtube Screengrab

Waiting to attack

Naval Headquarters now ordered the Western Fleet to hunt and destroy the enemy submarine detected in Indian waters near Diu. This order was passed on to the commander of the F-14 Squadron, Captain Mahendra Nath Mulla. The squadron was, however, now reduced to two anti-submarine frigates, the Kuthar not being available.

The two anti-submarine frigates left Bombay for their mission on 8 December and by the morning of 9 December were approaching the reported location of the enemy submarine. This was the ‘Hunter-Killer Force’ according to the TAS (Torpedo and Anti-Submarine specialists) of Western Naval Command! Due to its long-range detection capability, the Hangor detected the Khukri and the Kirpan much before these two ships were even aware that they were now close to their target. The Hangor came up to view the scene and dived down again and confirmed that the Khukri and the Kirpan were searching for her using the rectangular pattern of search, which is a well-known drill and known to all Commonwealth and NATO countries. Thus it was possible for the crew of the Pakistan submarine to anticipate and work out exactly where and when the Khukri and Kirpan would be at a particular point of time and when they would be most vulnerable. She positioned herself accordingly.

The Khukri and the Kirpan were in blacked-out condition, that is, no lights on these ships were visible. Unaware of the presence of the enemy submarine, they carried out their drills following the laid down rectangular pattern of search. Meanwhile the Hangor waited for them to come within the area most favourable for their destruction.

Hangor goes for the kill

On board the Khukri, Captain Mulla was having difficulty in coping with the experimental sonar, as this required him to reduce his speed to approximately 12 knots whereas, when conducting hunter-killer anti-submarine operations, speed was essential to out-manoeuvre and destroy a lurking submarine.

He was also aware that according to laid-down practice he was required to zigzag, a procedure to frustrate enemy submarine commanders. This was a tried and tested anti-submarine tactic but it required discipline and vigilance by all watch-keepers. The basic question was: would this not further lower the speed of the Khukri? Captain Mulla was already irked at having to restrict his speed from more than 14 to 10-12 knots. Would zigzagging be useful if his speed was further reduced? After all he was not evading the submarine, the basic purpose of zigzagging. On the contrary, he was charged to locate and destroy it. For that he needed maximum speed, already denied to him on account of the experimental sonar. He was, therefore, faced with two contradictory requirements – zigzagging to evade the submarine or speed to destroy it.

Commander Manu Sharma states the Khukri in fact was zigzagging and if zigzagging further reduced the speed of the Khukri then what speed was she doing when she was hit? Captain Mulla expressed his exasperation to Lieutenant Jain who decided to once again explain to him how the experimental sonar functioned. At this juncture Lieutenant Jain asked for some red and blue pencils to explain this on a chart. The Hangor, meanwhile, waited for the Khukri and the Kirpan to come to the anticipated location she had decided was the best to fire her torpedoes.

The first target, in fact, was not the Khukri but the Kirpan, the first to come within the designated target area. These torpedoes were meant to activate below the keel of the target ship so that it would break the keel and the ship would sink in minutes. The torpedo homed in to the Kirpan but failed to explode due to a faulty mechanism. With the firing of this torpedo, the position of the Hangor was given away and she had the choice of slipping away or staying on and firing another torpedo. Since both ships were still quite some distance away, the Hangor decided to fire another torpedo.

The Kirpan was now aware that she had been targeted and would, in fact, have heard the torpedo at least 1000 yards away and could, therefore, take evasive action. The Khukri, however, continued on its course and so the Hangor turned its attention to the Khukri and fired two more torpedoes, one at the Khukri and another at the Kirpan. The first probably exploded beneath the keel of the Khukri near the magazine, breaking it in two and activating the Khukri’s ammunition and the second aimed at the Kirpan did no damage perhaps due to the ability of the Kirpan to take evasive action. The Khukri sank in minutes. The time was 8.45 p.m. on 9 December 1971.

 This edited excerpt has been published from The Sinking of INS Khukri: Survivor’s Stories by Major General Ian Cardozo

Footnote: INS Khukri went down with 18 officers and 178 sailors, including its captain Mahendra Nath Mulla (awarded MVC posthumously). Young technical officer V.K. Jain, working with the experimental sonar, went down too.


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  1. Interesting to note that our military planners even then had the brilliant ability to start digging a well when the house was on fire ! If the whole world knew of the capabilities of the Pak submarines, why did we wait for the war to start before experimenting with new technologies ?

  2. I am confused, the pictures of INS Khukri shown in this article bear no resemblance to the Blackwood class of RN frigates that it was. Please explain.

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