A Chinese nuclear submarine docked in a Karachi harbour in May 2016 photographed on Google Earth.

Highlights Satellite image shows nuclear submarine docked at Karachi in 2016

China has been challenging India's dominance in Indian Ocean

Submarine at Karachi is China's most advanced

A Chinese Type 093 'Shang' class submarine, possibly the same boat to have docked in Karachi, spotted in the Malacca straits a month later in June 2016. (Source: @duandang)

Hours after NDTV reported that a Chinese nuclear submarine had been placed, through a satellite image, at Karachi last year, top sources in the Indian navy said that the submarine is from the most advanced and latest class built by China.The Type 093 Shang submarine, docked at the Karachi harbor, is likely being used to scrutinize the movements of Indian warships far more closely than ever before at a time when China is competing with India for domination of the Indian Ocean.Unlike conventional submarines, nuclear-powered submarines have an unlimited range of operations since their nuclear reactors rarely require to be refuelled. This means the submarines, which are armed with torpedoes and cruise missiles, can be deployed underwater for extended durations where they are difficult to track.The Karachi image was spotted first by a satellite imagery expert (Twitter handle @rajfortyseven) and can be accessed by clicking on the historical imagery icon on Google Earth and scrolling back to May 2016.The Chinese submarine at Karachi is estimated to displace 7,000 tonnes when it operates underwater and is armed with six torpedo tubes from which sophisticated anti-ship missiles can be fired. It's unclear if the submarine can also launch cruise missiles to hit targets on land. It is equipped with sophisticated sonars to detect and lock on to enemy ships and submarines. Chinese sources have indicated that the submarine is as quiet under water as variants of the US Navy Los Angeles Class, widely considered among the most silent and difficult to detect nuclear submarines.An image posted on twitter by Duam Dang, a journalist who works with the Vietnamese daily Thanh Nien, reportedly shows the same submarine returning to Chinese waters a month later (June 2016) while crossing through the Malacca Straits off the coast of Singapore.China's aggression in the Indian Ocean, strategically crucial for India's security, has been a growing concern. Last month, Navy Chief Admiral Sunil Lanba said, "As far as People's Liberation Army (PLA) Navy ships and submarines are concerned, the Indian Navy keeps a close eye and monitor their movements. We launch surveillance missions in the form of aircraft and ships to keep a track of them."For the last few years, the Indian Navy has been convinced that the presence of Chinese nuclear submarines in the Indian Ocean is part of a carefully-choreographed exercise to expand Beijing's military presence in the region. Senior Navy officers NDTV has spoken to reject China's earlier assertions that its submarine deployment has been in aid of the anti-piracy mission off the coast of Somalia.What is clear, however, is that a great game of underwater subterfuge, a feature of the Cold War, is presently underway in the Indian Ocean. To operate in the Indian Ocean, Chinese submarines need to sail through either the Malacca, Lombok or Sunda Straits where the shallow depth of the waters international regulations mean that they have to remain surfaced or visible.

This gives regional navies, including the Indian Navy, the ability to monitor the movement of Chinese submarines before they can dive to depths where tracking them is far more difficult. Indian Navy officers have told NDTV that the addition of the new version of the US-built P-8 aircraft have been a game-changer and a key asset in tracking Chinese submarines in the Indian Ocean. The P-8 is Washington's most advanced submarine-hunting weapon, equipped with sensors that can track and identify submarines by sonar and other means.Over the last decade, Pakistan has strengthened its naval links with China, its biggest international partner. In August last year, Pakistan State Radio announced a deal to acquire eight Chinese conventional diesel-electric powered submarines. The first four submarines are expected to be delivered by the end of 2023, while the others will be assembled in Karachi by 2028. Perhaps most significantly, China has access to Pakistan's strategic Gwadar port, central to the $46 billion China-Pakistan Economic Corridor (CPEC) that is under development, in addition to its own recently constructed naval base in Djibouti situation in the Horn of Africa.