The Sinking of INS Khukri

This article has also been published in the Society of Twentieth Century Wargamers Journal.

INS Khukri

INS Khukri (Indian Navy, CC-BY via Wikipedia)

On December 9th, 1971, the Indian frigate INS Khukri was sunk by the Pakistani submarine PNS Hangor. To date, the Khukri is the only Indian warship to have been lost in action. It was built in the UK, and was basically a British Type 14 (Blackwood) frigate modified to suit Indian requirements. At the time it was sunk, the Khukri had an extra device fitted to its 170/174 sonar, which was intended to improve the detection range. Commissioned in December 1969, the Hangor was a French Daphne class submarine, well equipped with modern sensors and weapons.

On December 7/8th, Indian intelligence picked up transmissions from a Pakistani submarine 35 miles south-west of Diu Head, and the 14th Frigate Squadron was detailed to find and sink the submarine. The squadron normally consisted of three ships (Kirpan, Khukri and Kuthar), but Kuthar was being repaired in Bombay after suffering a boiler room explosion. The frigates did not have helicopters on board, and no helicopter or fixed-wing air support was available for the operation. In the early hours of December 9th, the Hangor picked up two sonar contacts. Their sonar and radar transmissions identified them as warships, but Hangor failed to intercept them, and lost contact when the range became too great. Analysis of the ship’s movements revealed that they were engaged in a rectangular anti-submarine search, and so Hangor manoeuvred to a point judged likely to be in the ships’ path.

By 19:00 Hangor was in position and the two Indian surface ships were approaching on a steady course with a narrow weave, at a speed of 12 knots. The Khukri’s captain had ordered a slow speed to help improve the sonar’s detection range, despite this being against Indian antisubmarine doctrine. Hangor went to action stations at 19:15. At 19:30 she came to periscope depth. The radar showed the range to be 9,800 metres, but the ships were darkened and could not be seen, so the decision was made to dive to 55 metres and rely exclusively on sonar for the approach and attack. Still undetected by the Indian ships, at 19:57 Hangor fired a torpedo at Kirpan. The torpedo failed to explode, but was detected by Kirpan, who turned away and fired anti-submarine mortars. Khukri increased speed and turned towards Hangor, who fired a second torpedo at Khukri. After five minutes, this torpedo exploded under the Khukri’s oil tanks, and she began to sink.

A few minutes later, Kirpan turned back to attack the Hangor with depth charges (her anti-submarine mortars had broken down) and the Hangor fired another torpedo at Kirpan before turning away and exiting at maximum speed. Kirpan outran the torpedo and later returned with another ship, INS Katchal, to rescue Khukri’s survivors.

Following the attack, the Indian Navy and Air Force mounted Operation Falcon, a major anti-submarine operation involving ASW ships, Sea King helicopters and Alize ASW/strike aircraft. The Hangor detected 36 salvoes of depth charges during the four day operation, but only two were close enough to shake the submarine, which returned to Karachi on 18th December.

As well as the obvious loss to the Indian Navy of a frigate, the sinking of the Khukri had further-reaching consequences. Morale in the Pakistani Navy improved after news of the sinking was received, the Indian Navy cancelled an operation that was due to start on 10th December, and Operation Falcon tied up a large number of ships, helicopters and aircraft for four days.

INS Khukri & INS Kirpan

Indian Navy crest

Indian Navy crest (CC-BY-SA: Chanakyathegreat)

Displacement: 1,180 tons standard, 1,456 full load
Length: 300 feet (91.4m) pp, 310 feet (94.5m) oa
Beam: 33 feet (10 m)
Draught: 15.5 feet (4.7m)
Speed: 27.8 knots maximum, 24.5 knots sustained
Oil fuel: 300 tons
Complement: 150
Sensors: S band air & surface surveillance radar

Armament:
3x single 40rnm AA guns
2x Limbo 3-barrelled depth charge mortars
Provision was also made for 2x twin 21 inch torpedo tubes, but they were not fitted.

PNS Hangor

Pakistan Navy emblem

Pakistan Navy emblem

Displacement: 700 tons standard, 1,043 tons submerged
Length: 57.75m
Beam: 6.75m
Draught: 4.56m
Speed: 13.5 knots surfaced, 16 knots submerged
Complement: 50

Sensors:
1x Thomson-CSF surface search radar
1x Thomson-Sintra DSUV-1 passive search sonar
1x Thomson-Sintra DUAA-1 passive search/attack sonar

Armament:
8x 550mm torpedo tubes (forward)
4x 550mm torpedo tubes (aft)
No reloads are carried for the torpedo tubes