Operation Trident was an offensive operation launched by the Indian Navy on Pakistan's port city of Karachi during the Indo-Pakistani War of 1971. Operation Trident saw the first use of anti-ship missiles in combat in the region. The operation was conducted on the night of 4–5 December and inflicted heavy damage on Pakistani vessels and facilities. While India suffered no losses, Pakistan lost a minesweeper, a destroyer, a cargo vessel carrying ammunition, and fuel storage tanks in Karachi. Another destroyer was also badly damaged and eventually scrapped. India celebrates its Navy Day annually on 4 December to mark this operation. Trident was followed up by Operation Python three days later

In 1971, the Port of Karachi housed the headquarters of the Pakistan Navy, and almost its entire fleet was based in Karachi Harbour. Since Karachi was also the hub of Pakistan's maritime trade, a blockade would be disastrous for Pakistan's economy. The security of Karachi Harbour was predominant to the Pakistani High Command, and it was heavily defended against any air or naval strikes. The strike aircraft based at airfields in the area secured the port's airspace.

Towards the end of 1971, there were rising tensions between India and Pakistan, and after Pakistan declared a national emergency on 23 November, the Indian Navy deployed three Vidyut-class missile boats in the vicinity of Okha, near Karachi, to carry out patrols. As the Pakistani fleet would also operate in the same waters, the Indian Navy set a demarcation line that ships in their fleet would not cross. Later, this deployment proved useful for gaining experience in the region's waters. On 3 December, after Pakistan attacked Indian airfields along the border, the Indo-Pakistani War of 1971 officially began.^{[non-primary source needed]}

While Operation Trident was primarily a naval strike, the Indian Air Force also conducted critical bombing raids on Karachi harbour facilities, oil tanks, and infrastructure. These joint efforts significantly impaired Pakistan’s maritime logistics. The humour-laced term "Karachi Halwa" was later coined informally to describe the destructive sweet mix they delivered over Karachi.

The Indian Naval Headquarters (NHQ) in Delhi, along with the Western Naval Command, planned to attack the Port of Karachi. A strike group under Western Naval Command was formed for this mission. This strike group was to be based around the three Vidyut-class missile boats already deployed off the coast of Okha. However, these boats had limited operational and radar range, and to overcome this difficulty, it was decided to assign support vessels to the group.

On 4 December, what was now designated as the Karachi Strike Group was formed and consisted of the three Vidyut-class missile boats: INS Nipat, INS Nirghat and INS Veer, each armed with four Soviet-made SS-N-2B Styx surface-to-surface missiles with a range of 40 nautical miles (74 km; 46 mi), two Arnala-class anti-submarine corvettes: INS Kiltan and INS Katchall, and a fleet tanker, INS Poshak. The group was under the command of Commander Babru Bhan Yadav, the commanding officer of the 25th Missile Boat Squadron.

As planned, on 4 December, the strike group reached 250 nautical miles (460 km; 290 mi) (nmi) south off the coast of Karachi and maintained its position during the day, outside the surveillance range of the Pakistan Air Force. As Pakistani aircraft did not possess night-bombing capabilities, it was planned that the attack would take place between dusk and dawn. At 10.30 pm Pakistan Standard Time (PKT), the Indian task group moved 180 nmi (330 km; 210 mi) from its position towards the south of Karachi. Soon, Pakistani targets, identified as warships, were detected 70 nmi (130 km; 81 mi) to the northwest and northeast of the Indian warships.

INS Nirghat sailed forward in a northwesterly direction and fired its first Styx missile at PNS Khaibar, a Pakistani Battle-class destroyer. Khaibar, assuming it was a missile from Indian aircraft, engaged its anti-aircraft systems. The missile hit the right side of the ship, exploding below the galley in the electrician's mess deck at 10.45 pm (PKT). This led to an explosion in the first boiler room. Subsequently, the ship lost propulsion and was flooded with smoke. An emergency signal that read: "Enemy aircraft attacked in position 020 FF 20. No. 1 boiler hit. Ship stopped", was sent to Pakistan Naval Headquarters (PNHQ). Due to the chaos created by the explosion, the signal contained the wrong coordinates of the ship's position. This delayed rescue teams from reaching its location. Observing that the ship was still afloat, Nirghat fired its second missile, hitting Khaibar in the second boiler room on the ship's starboard side, eventually sinking the ship and killing 222 sailors.