The tug-of-war over the South China Sea is seen mainly as a struggle among rival claimants - China, Taiwan and several South-East Asian states - for control of valuable fisheries as well as sea bed oil, natural gas and mineral resources.
China's claim to about 80 per cent of the 3.5 million square kilometre sea and its hundreds of atolls, rocks and reefs, has also alarmed outside seafaring and trading nations, including the United States, Australia and Japan.
They regard the South China Sea as an international maritime highway with free navigation for seaborne trade, unimpeded movement of naval vessels, and unfettered over-flight for military aircraft.
But recent developments in China's nuclear weapons program suggest there is another important dimension to China's increasing assertiveness in enforcing its claimed jurisdiction in the semi-enclosed sea: protecting a new generation of nuclear-powered submarines armed with atomic warheads and based at Sanya on China's Hainan Island.
Okazaki Institute in Tokyo special research fellow Tetsuo Kotani says, ''Without understanding the nuclear dimension of the South China Sea disputes, China's maritime expansion makes little sense.''
One of the new generation subs was first spotted by a commercial satellite at Sanya in 2008. It was tied up to a pier that analysts said was China's first and so far only demagnetising facility for submarines. Demagnetisation is conducted before deployment to remove residual magnetic fields in the metal of a sub to make it harder to detect by hostile submarines, surface ships and anti-submarine aircraft.
Initially, these new generation Chinese subs and the nuclear-tipped ballistic missiles they could launch while submerged would be able to target potential adversaries in the Asia-Pacific and US bases in the region.
Eventually, with longer-range intercontinental missiles, they could cover the whole of the US from launch points in the deep waters of the South China Sea without having to venture too far from their rock shelter tunnels bored into a mountain that forms part of the Sanya naval base for China's South Sea Fleet. This would give China a more effective deterrent against nuclear attack, one that operated from under the sea in addition to land-based nuclear missiles.
In recent years, China has built up a relatively small but increasingly impressive arsenal of approximately 140 nuclear ballistic missiles either concealed in silos or mounted on special launch vehicles and moved around to different hiding places on land.
Each carries a single nuclear warhead. But earlier this month, a newspaper controlled by the ruling Chinese Communist Party reported that China was developing the capability to do what Russia and the US have the technology to do - put multiple warheads on its intercontinental ballistic missiles, each capable of hitting different targets. This could greatly increase the number of China's operational nuclear weapons and overwhelm any missile defence system.
At the same time, China is building a fleet of new JIN-class nuclear-powered ballistic missile submarines (SSBNs), known as Type-094. Two are in operation, a third is under construction and may already have been launched, and at least two more are expected to be built.
Meanwhile, China is hoping to complete testing of the JL-2 nuclear-tipped missile for the Type-094 sub, which can carry 12 of the missiles. The US Defence Department's annual report to Congress in May on China's armed forces and military strategy noted that the while the JL-2 program had faced repeated delays, it ''may reach initial operating capability'' within the next two years, giving the Chinese Navy ''its first credible sea-based nuclear'' deterrent.
In addition to adding a nuclear dimension to China's interests in the South China Sea, having a sea-based nuclear deterrent may pose serious control problems for the Central Military Commission which supervises the country's nuclear arsenal. The commission and the Chinese Navy have no experience in operating SSBNs in either peacetime or during a crisis. Yet remaining submerged and out of communication for lengthy periods is essential if SSBNs are to remain undetected.
So for the foreseeable future, China's land-based nuclear missile force is expected to be the mainstay of the country's deterrent and retaliatory strike capability against the continental US or other faraway targets.
But that will be cold comfort for any regional adversary of China that might soon be targeted by a new SSBN fleet armed with nuclear ballistic missiles.
The writer is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore.