To the alarm of India, China is waging a submarine sales offensive at bargain prices to nations with Indian Ocean coastlines

To date, Bangladesh, Pakistan and Thailand have either purchased or agreed to acquire Chinese submarines.

China's aggressive marketing of submarines has got India worried about Beijing's intentions in light of the Asian power's steady maritime advances in the region, as well as Pacific waters.

Bangladesh was first to take advantage of the cut-price submarines offered by China by acquiring two used Ming-class diesel-powered vessels in 2013. Bangladesh began operating them in March 2017.

One local military source put the cost of each submarine at $100 million, or one-tenth of the price of a new European submarine.

In April 2017, Thailand agreed to purchase two newly constructed subs in the Yuan class, which is two classes more advanced than the Ming sub. A Thai government source said each sub will cost about 13.5 billion baht (47 billion yen, or $424 million).

Defense Minister Gen. Prawit Wongsuwan said it is far less expensive than submarines of other countries.

Bangkok is also considering purchasing two more.

During Chinese President Xi Jinping's visit to Pakistan in 2015, it was proposed that Islamabad acquire eight Chinese submarines. China the following year confirmed that such a plan existed. The eight will be Yuan-class subs, four of which will be constructed in Pakistan.

Since the 21st century dawned, China has shifted its maritime military strategy from one focused on defending its near seas to one that covers far seas extending to the Pacific and Indian oceans. That shift has led to an increased emphasis on aircraft carriers and submarines. Beijing deployed both types of vessel from around 2013 to the Indian Ocean ostensibly for anti-piracy efforts off Somalia.

The purchase of Chinese submarines has a spin-off benefit in that it allows Beijing to extend its influence in related fields. For example, harbors capable of hosting the submarines will be constructed.

Purchasing nations must also install repair and supply facilities that match specifications required for handling the Chinese submarines.

This gives China the option of asking that its submarines be allowed to temporarily berth there for repairs or to acquire weapons.

The more submarines China sells to nations in the region, the more data it will accumulate related to operations and malfunctions that could be used to improve submarine technology, experts said.

Once a submarine is purchased, the nation in question must rely on Chinese naval officers and technicians for instructions on operating the vessel. Those personnel could also play a key role in gathering vital information, including seabed mapping, as China strives to improve its submarine capabilities.

In addition, military media have reported that Egypt and Cuba are among other nations that have also expressed an interest in Chinese submarines.

India is concerned about possible security ramifications.

According to Indian military sources, the Chinese Navy has been operating submarines since 2013 in the Indian Ocean. Those voyages occur twice a year and typically last three months or so.

If neighboring nations acquire Chinese submarines, there is the possibility that Chinese naval instructors could be on board while those vessels operate in waters near India.