The last time Chinese warships sailed to Africa was some 600 years ago, when a fleet com- manded by Admiral Zheng, a Ming dynasty eunuch, arrived on a diplomatic mission. This week two Chinese destroyers and a supply vessel are also due to set out for the Gulf of Aden, where they will join an international armada attempting to clear vital sea lanes of Somali pirates.

The expedition marks an important evolution in Beijing's diplomacy. China has taken part in several international peacekeeping operations, but until now it has kept its troops in its own neighbourhood, reflecting a longstanding policy of non-interference in other countries' affairs. The expedition to the waters off Somalia, however, is intended not only to protect Chinese vessels vulnerable to attack by pirates, but also to project its growing military power overseas in a way that does not antagonise its neighbours or cause concern in Washington.

China can now demonstrate its maturity as a world power by assuming a seemingly selfless responsibility for global security. This, it knows, will be welcome to fellow members of the UN Security Council. It has chosen its moment well. There is little likelihood that the ships will be engaged in hostilities. At the same time India, which may look with alarm at this projection of power by its Asian rival in an ocean that laps its own shores, has little option but to offer a formal welcome. China is now giving help to an international force in which India is also engaged. Japan, too, will find it hard to give public expression to its own misgivings. Beijing's naval commitment stands in contrast to Tokyo's constitutional restrictions on sending its defence forces overseas. And although Japan has recently extended its naval mission backing the US operations in Afghanistan, it will hardly feel easy at the more activist posture of its large neighbour.

Altruism is not the only motivating factor, however. China has a large and growing economic interest throughout Africa. It has tried to keep its trade and oil activities separate from any political commitments, refusing to condemn some of the unsavoury regimes with whom it trades. This has opened doors across the continent. But it has provoked noisy opposition in the West, where public opinion has accused China of condoning the massacres in Darfur, propping up totalitarian regimes and offering a lifeline to President Mugabe in Zimbabwe. China has therefore been eager to demonstrate a “principled” engagement in Africa - but with a pragmatism that does not affect its interests. Somalia, a state beyond rescue by the African Union, offers a perfect opportunity.

At least seven ships flying the Chinese flag or carrying Chinese crew have been hijacked since January. The crew of a Chinese cargo ship fought off pirates in the Gulf of Aden last Wednesday. Clearly, China's growing trade with Africa makes it especially vulnerable. To an African audience, however, China can offer a more persuasive argument. Somali pirates also imperil their own country's recovery by seizing foreign ships carrying vital food and provisions to the war-torn cities of Somalia itself. China can therefore present itself as the champion of humanitarian relief. And if this gives it a face-saving way of renewing military exchanges between Beijing and Washington, broken over US support for Taiwan, China can claim a bonus.