India is speeding up a navy modernization program and leaning on its neighbors to curb Chinese submarine activity in the Indian Ocean, as nations in the region become increasingly jittery over Beijing's growing undersea prowess.
Just months after a stand-off along the disputed border dividing India and China in the Himalayas, Chinese submarines have shown up in Sri Lanka, the island nation off India's southern coast. China has also strengthened ties with the Maldives, the Indian Ocean archipelago.
China's moves reflect its determination to beef up its presence in the Indian Ocean, through which four-fifths of its oil imports pass, and coincides with escalating tension in the disputed South China Sea, where Beijing's naval superiority has rattled its neighbors.
"We should be worried the way we have run down our submarine fleet. But with China bearing down on us, the way it is on the Himalayas, the South China Sea and now the Indian Ocean, we should be even more worried," said Arun Prakash, former chief of the Indian navy.
"Fortunately, there are signs this government has woken up to the crisis," he said. "But it will take time to rebuild. We should hope that we don't get into a face-off with the Chinese, that our diplomacy and alliances will keep things in check."
Prime Minister Narendra Modi's government has ordered an accelerated tendering process to build six conventional diesel-electric submarines at an estimated cost of 500 billion rupees ($8.1 billion), in addition to six similar submarines that French firm DCNS is assembling in Mumbai port to replace a nearly 30-year-old fleet hit by a run of accidents.
The country's first indigenously built nuclear submarine - loaded with nuclear-tipped missiles and headed for sea trials this month - joins the fleet in late 2016. India leased a nuclear-propelled submarine from Russia in 2012 and is in talks to lease a second one, navy officials told Reuters.
The government has already turned to industrial group Larsen & Toubro Ltd, which built the hull for the first domestic nuclear submarine, to manufacture two more, sources with knowledge of the matter said.
Elsewhere in the region, Australia is planning to buy up to 12 stealth submarines from Japan, while Vietnam plans to acquire as many as four additional Kilo-class submarines to add to its current fleet of two. Taiwan is seeking U.S. technology to build up its own submarine fleet.
Japan, locked in a dispute with China over islands claimed by both nations, is increasing its fleet of diesel-electric attack submarines to 22 from 16 over the next decade or so.
In addition to the leased Russian nuclear-propelled submarine, India's navy currently has 13 ageing diesel-electric submarines, only half of which are operational at any given time due to refits. Last year, one of its submarines sank after explosions and a fire while it was docked in Mumbai.
China is estimated to have 60 conventional submarines and 10 nuclear-powered submarines, including three armed with nuclear weapons.
Ma Jiali, an expert at the China Reform Forum's Centre for Strategic Studies which is affiliated with the Central Party School, said Beijing's top concern in the Indian Ocean was safeguarding the passage of its commodities, especially oil.
"There are many voices in India who believe the Indian Ocean belongs solely to India, and no other country belongs there. That line of thought is common - but of course it shouldn't be viewed like that. Our (China's) view is that there should be dialogue and discussion between China and India."
With India building its navy to about 150 ships, including two aircraft carriers, and China holding around 800 in its naval fleet, the two are more likely than not to run into each other, naval officials and experts say.
David Brewster, a strategic affairs visiting fellow at the Australian National University, said India will do everything it can to recover its dominant position in the Indian Ocean.
It may seek naval cooperation with Japan and Australia, and expand a military base on the Andaman Islands which lie about 140 km (87 miles) from the Malacca Straits, he said.
"India sees the presence of any Chinese naval vessel as an intrusion. There is a big ramp-up in their presence, which is clearly intended to send a message to India," said Brewster.
India has engaged in intense diplomacy with Sri Lanka about the Chinese submarine presence, reminding it that New Delhi must be informed of such port calls under a maritime pact they signed this year along with the Maldives.
India has also muscled into an $8 billion deep water port that Bangladesh wants to develop in Sonadia in the Bay of Bengal, with the Adani Group submitting a proposal in October. China Harbor Engineering Company, an early bidder, was the front-runner.
"If China continues down this path and continues with this level of presence in the Indian Ocean then the Indians will feel they need to respond," said Brewster.