The eight submarines are being built with Chinese assistance

Thursday marked the 50th anniversary of the sinking of an Indian Navy warship, INS Khukri, by a Pakistani submarine in the 1971 war. The death of 194 officers and sailors on the Khukri remains the Indian Navy's worst disaster.

The INS Khukri was a frigate, a warship meant for multiple roles, that was acquired from the UK. The Pakistan Navy submarine that sank the Khukri was the PNS Hangor, a diesel-electric submarine built in France. The PNS Hangor was then a brand-new vessel, having entered service in 1970. The PNS Hangor was decommissioned in 2006.

The Pakistan Navy has been celebrating December 9 as Hangor Day to mark the sinking of the INS Khukri.

A message by the chief of the Pakistan Navy Admiral Muhammad Amjad Khan Niazi on the occasion of Hangor Day was shared by the service on its Twitter handle. In the message, Niazi referred to the construction of eight diesel-electric submarines that the Pakistan Navy designated as the Hangor class in memory of the original ship.

Niazi said the fifth vessel of the class would be named PNS Tasnim in honour of retired admiral Ahmad Tasnim, who was commander of the PNS Hangor when it sank the INS Khukri.

Chinese Design

The eight submarines are being built with Chinese assistance. The deal between the two nations envisages construction of the first four submarines in China and the remainder in Karachi under transfer of technology. The fifth submarine appears to be one that will be built in Pakistan. Interestingly, the Pakistan Navy on Thursday held a steel-cutting ceremony for a Hangor class submarine in Karachi, marking start of construction.

The first of the new submarines are expected to enter service by 2022, with the units being built in Karachi slated to finish construction by 2028.

The new Hangor class of submarines are expected to have an air-independent propulsion system that would enable them to spend more time underwater without needing to resurface to recharge their batteries.

There has been speculation Pakistan could arm the new Chinese-built vessels with cruise missiles capable of carrying nuclear warheads.

The sinking of the INS Khukri in 1971 was a watershed, marking the first destruction of a surface ship by a submarine since the Second World War.