COMMUTERS BETWEEN MARIN COUNTY and San Francisco in northern California are getting used to a new spectacle during rush hour. Vast, ungainly container ships, bearing China’s flag and name, plough along under the glorious Golden Gate Bridge. They are bringing goods into the Port of Oakland—and taking back America’s trade deficit. Any pleasure yachts zipping around the bay give them a wide berth.

This is China as a Pacific power, a commercial rather than a naval one. According to statistics gathered by Michael McDevitt, a retired rear-admiral at America’s Centre for Naval Analyses, it is now the world’s largest shipbuilder; has the third-largest merchant marine, and by far the largest number of vessels flying its own flag; and boasts a 695,000-strong fishing fleet. It accounts for about a quarter of the world’s container trade. And almost all the steel boxes shipped on the world’s oceans are made in China, too.

Much of the security of that trade across the Pacific is the gift of America. China “free-rides” on the protection provided by the United States Pacific Fleet, based in Pearl Harbour, Hawaii, so it benefits from America’s enforcement of the rules of sea-based activity. But in the western Pacific China has behaved provocatively towards some staunch American allies, testing the bounds of international maritime law.

That implicit challenge comes up often in speeches by American officials. Whether civilian or military, they use an oddly terrestrial metaphor when discussing America’s leadership in the world’s biggest ocean. It is all about enforcing “the rules of the road”, they say. One set of those rules are those on trade, which, as discussed in the previous article, America hopes to modernise via the Trans-Pacific Partnership (TPP). Another is about maritime security, particularly in the sea lanes through disputed territorial waters in what China calls its “near seas”. America argues that to safeguard those vital routes of commerce, any territorial quarrels should be settled according to international law, not by force and intimidation. Otherwise, says Daniel Russel, assistant secretary of state for Asia-Pacific, it is a dangerous world where “might makes right.”

However, as Henry Kissinger writes in his new book, “World Order”, China does not necessarily see the rules the way America does: “When urged to adhere to the international system’s ‘rules of the game’ and ‘responsibilities’, the visceral reaction of many Chinese—including senior leaders—has been profoundly affected by the awareness that China has not participated in making the rules of the system.”

Mr Kausikan of the Singapore foreign ministry goes further. He says that all Chinese are aware of the 100 years of invasion by Western powers and Japan that their country suffered before 1949. “It was never very realistic to expect China to be a ‘responsible stakeholder’ in a regional and global order that it had no say in establishing and which it holds responsible for a century of humiliation,” he says.

American officials acknowledge that China plays by many global rules, especially the trade ones it signed up to when joining the World Trade Organisation in 2001. But especially in its own neighbourhood, it is challenging rules and norms—including some it has explicitly agreed to—that have kept the seas safe since the second world war.

For instance, in 2002 it signed a treaty with its neighbours in ASEAN agreeing to settle maritime disputes in the South China Sea peacefully and according to international law, such as the 1982 United Nations Convention on the Law of the Sea (UNCLOS). Yet it is in often tense disputes with ASEAN countries such as Vietnam and the Philippines over control of three sets of islands and rocks in the South China Sea—the Paracel Islands, the Spratly Islands and Scarborough Shoal—and with Japan over the Senkaku/Diaoyu Islands. When the Philippines took its opposition to China’s maritime claims to UNCLOS in March, China huffily refused to accept the arbitration.

It has also sought to stop American naval and air-force vessels operating in its exclusive economic zone (EEZ), 200 nautical miles from its shoreline (see map), which America and many of its allies consider a violation of UNCLOS. In August this year a Chinese fighter intercepted an American Navy P-8 maritime patrol in international airspace about 135 miles (216km) off Hainan Island, which the Department of Defence described as “very, very close, very dangerous”.

This EEZ dispute could have profound implications for the stability of trans-Pacific sea routes, overseen for generations by America’s navy. “It may sound arcane,” writes Bill Hayton, author of “South China Sea: The Struggle for Power in Asia”, published earlier this year, “but the legal debate over what one country’s military vessels can do in another country’s [EEZ] has already brought the United States and China to the edge of conflict. It’s a battle between American demands for access to the ‘global commons’ and China’s search for security. It’s a struggle that will define the future of Asia and possibly beyond.”

The South China Sea is where that struggle is most visible. On modern maps the reefs and shoals between China, Vietnam, the Philippines, Taiwan and Malaysia are labelled “Dangerous Ground”—not because of their disputed ownership but because through history they have been a mariner’s nightmare.

According to Mr Hayton, the South China Sea itself plays an historic role in the crafting of the rules in contention. In 1603 the Dutch East India Company seized a Portuguese ship laden with raw silk and gold near the Strait of Malacca and hired a Dutch jurist, Hugo Grotius, to defend its action. He wrote a book in Latin called “Mare Liberum” (“The Free Sea”), arguing that the seas were international territory and should be open to all. Over the following centuries this was used by global powers as justification to sail merchant vessels where they liked, often with gunboats sailing alongside to enforce their authority.

Go by the book

Built loosely on “Mare Liberum”, UNCLOS established the EEZ concept which gave coastal nations exclusive rights over natural resources within a 200 nautical-mile limit but allowed for free navigation and overflights outside territorial waters extending to 12 nautical miles from the coast. Ironically, China has ratified UNCLOS whereas the American Senate has not—though in practice the American navy follows and attempts to enforce it.

But China’s interpretation (and that of a small group of large developing countries such as India and Brazil) differs from that of most states: it requires naval vessels to seek its permission before entering its EEZ. In 2013 a Chinese navy ship cut directly across the path of the United States Navy cruiser Cowpens, forcing it to change course abruptly to avoid a collision. Such incidents are red rags to the Americans. Their navy still regularly sends spy ships into China’s EEZ.

If China were to decide to enforce its version of the rules, the risks would be severe. In his book, “Fire on the Water: China, America and the Future of the Pacific”, Robert Haddick said it could mean the exclusion of foreign warships “from the Strait of Malacca all the way to Japan’s home islands”. Even if China were to keep the seas open to merchant shipping, the whole concept of maritime security would be jeopardised. America might be forced to retaliate.

Vast, ungainly container ships, bearing China’s flag and name, plough along under the glorious Golden Gate Bridge

That is an alarming scenario, though many security specialists say China does not seem to be spoiling for such a showdown with America, at least not yet. Optimists reckon that the Chinese navy, though growing fast, is ill-prepared for war with such a doughty opponent. Moreover, a defeat would be catastrophic for China. Security analysts say the Communist Party would lose its legitimacy and the trade-driven economy would collapse.

Pessimists argue that, even with good intentions on both sides, miscalculation or misunderstanding could still lead to conflagration. Chuck Hagel, America’s defence secretary, says America will oppose any effort to restrict overflight or freedom of navigation. It will “not look the other way”, he told his defence counterparts at the Shangri-La Dialogue in May.

In its island disputes, security analysts say China is picking fights with American allies that test the United States’ commitment to upholding the law by proxy, in steps small enough to make retaliation hard. But in the process it is gradually establishing “facts on the ground” in its own back pond. Euan Graham of the Singapore-based S. Rajaratnam School of International Studies says that eventually these could enable it to thicken its EEZ into a robust coastal buffer. He notes that Chinese history—such as Britain’s shameful Opium wars of the 1840s and 1850s—makes the country particularly sensitive to maritime threats.

That dashed line

All the disputed territories fall within what China calls its nine-dash line, which covers virtually all of the South China Sea and more than half of its neighbours’ own EEZs. Since it took over Mischief Reef in 1995, China has quarrelled with Vietnam over the Spratly Islands and installed some garrisons. It also occupied Scarborough Shoals after a stand-off with the Philippines in 2012. This year drilling by a big Chinese oil firm in waters 120 nautical miles (222km) from the Vietnamese coast sparked anti-Chinese riots in Vietnam. Tensions over the Senkaku/Diaoyu islands have been hurting relations with Japan since 2010.

Mr Haddick refers to China’s tactic of gradually enforcing these island claims as “salami-slicing”. It is “the slow accumulation of small changes, none of which in isolation amounts to a casus belli, but which can add up over time to a significant strategic change”. Ronald O’Rourke, a naval analyst for the United States Congressional Research Service, says Chinese officials have called it a “cabbage strategy”. The islands are wrapped, cabbage-like, in successive layers of protection formed by fishing boats, Chinese coast guard ships and finally naval vessels. China rarely deploys its armed forces in these creeping encroachments. Instead, says Ian Storey of the Institute of South-East Asian Studies, it uses maritime law-enforcement agencies. “Even the name implies China already feels it has jurisdiction.”

The tactic makes it harder for any claimant to launch a military response without appearing to raise the ante. “The Chinese are pursuing a pretty clever strategy and the rest of us haven’t figured out a good response,” says Admiral Dennis Blair, former head of America’s forces in the Pacific and now chairman of the Sasakawa Peace Foundation USA. He reckons that countries threatened by China’s “administrative aggression” should settle their territorial disputes with each other first and then present a united front to China. Mr Russel says “it is a good thing that China is not deploying the People’s Liberation Army’s navy.” But he points out that “whatever is driving the behaviour, the point is that it risks escalation and confrontation, so the exercise of restraint is necessary.”

In late September more than 18,000 American army, navy, air force and marine corps personnel took part in an unprecedented joint exercise off the Pacific island of Guam. Without explicitly saying so, it was aimed at testing responses to the sort of “sea-denial” strategy (missiles, submarines and cyber-attacks) that American military planners think China has developed to counter naval threats. According to Rear-Admiral Mark Montgomery, a Seventh Fleet commander, a Chinese auxiliary ship was spotted observing the exercises in America’s EEZ. That was the second time this year a Chinese vessel was seen snooping in American waters during war games. The Americans chose to treat it as a possible sign that China was exploring the benefits of their version of the UNCLOS rules.

Earlier this year naval chiefs from China, America and many other countries pulled off a surprise by signing the Code for Unplanned Encounters at Sea, which provides guidelines for naval ships or aircraft when they unexpectedly come close to each other. It offers a measure of potential damage control but it is not legally binding, nor does it apply in a country’s territorial waters, so it may be interpreted as subjectively as UNCLOS.

For China, the big question as it seeks to become a maritime power is how much it wants to project that status into the wider oceans beyond its neighbourhood. Singapore’s Mr Kausikan asks whether China will support a system that has benefited it or continue to be a “global free-rider”. That question is looming larger in the maritime sphere. As America becomes less reliant on Middle Eastern oil, thanks to its shale revolution, will China help to protect the sea lanes across the Indian and Pacific oceans for everyone’s benefit?

Next in our special report on the Pacific Age:

North American energy: Oil and water (6/9)