China has caused alarm around the region and in Washington because of its ambitious military modernization program, especially with this week's announcement of a test flight of a stealth fighter.

China says it needs to upgrade its outmoded forces and its plans are not a threat to any country.

U.S. Defense Secretary Robert Gates urged deeper military contacts between the two countries on a visit to China this week.

Here are some facts about China's military modernization and some of the weapons systems that have attracted attention:

AIR FORCE:

- Along with the development of its aeronautics industry, China has developed a more formidable design capacity. Its most advanced aircraft in service, and for the United States the potentially most threatening, are Russian Su-30 and Su-27 fighters. China is developing its fourth-generation J-11.

- China confirmed it held its first test-flight of the J-20 stealth fighter jet on Tuesday, a show of muscle during a visit by Gates aimed at defusing military tensions between the two powers.

- Some analysts have said that the development of the J-20 is a strong indicator that China is making faster-than-expected progress in developing a rival to Lockheed Martin's F-22 Raptor, the world's only operational stealth fighter designed to evade detection by enemy radar.

- However, deployment is likely to be years away and Gates said ahead of his visit to China that he thought there was some question as to just how stealthy it really was.

- Modernization has also included developing an inflight refueling capacity, to give its fighters a greater reach, and early warning aircraft.

NAVY:

- President Hu Jintao has made the navy's modernization a priority. It is upgrading its destroyers and frigates to range further and strike harder.

- China could launch its first aircraft carrier this year, according to Chinese military and political sources, a year earlier than U.S. military analysts had expected, underscoring its growing maritime power and assertiveness.

- The cost of building a medium-sized conventionally powered, 60,000-tonne carrier similar to the Russian Kuznetsov class is likely to be more than $2 billion. China is likely to acquire at least two.

- China is building new Jin-class ballistic missile submarines, capable of launching nuclear warheads while at sea. It has built a naval base on Hainan, the island-province in the south, that can serve submarines.

MISSILES:

- U.S. officials have taken note of disclosures in recent weeks of advances in China's capabilities, including in its anti-ship ballistic missile program, which could challenge U.S. aircraft carriers in the Pacific.

- The successful missile kill of an old satellite in early 2007 represented a new level of ability for the Chinese military, and last January China successfully tested emerging technology aimed at destroying missiles in mid-air.

ARMY:

- China is trying to transform the 2.3 million-strong People's Liberation Army into a smaller, sleeker modern force capable of short, high-intensity conflicts against high-tech adversaries.

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