WASHINGTON - The United States was taken by surprise over Chinas first stealth fighter, which the Asian nation rolled out on Wednesday. a top American naval official said. At the same time, Vice Admiral David Dorsett, the director of US naval intelligence, downplayed Washingtons concerns, saying it would be years before Chinas new fighter would be operational. But he did admit that the US had been surprised by the pace of some of Chinas military development. On the eve of US Defence Secretary Robert Gatess visit to Beijing, photographs indicated a prototype of the J-20 had been completed after tests last week at an airfield in southwestern China. Developing a stealth capability with a prototype and then integrating that into a combat environment is going to take some time, he said. Dorsett said he was not surprised the Chinese were developing a stealth fighter to rival Americas fifth generation F-22 Raptor. Military analysts warn that China is developing a new version of its Dongfeng 21 (DF-21D) ballistic missile that could pierce the defences of even the sturdy US naval vessels and has a range far beyond Chinese waters. We underestimated when they would be competent and capable of delivering a technological weapon of that type, Dorsett told reporters. The naval intelligence chief said he was more concerned about Chinas efforts in cyber-warfare and developing its capabilities in space. Chinas Global Times reported on the J-20 fighters runway test at the Chengdu Aircraft Design Institute in southwest China, according to media reports. Photos also appeared on unofficial military Web sites and blogs. The plane could be flight-tested as early as Thursday, observers said. Deputy air force chief He Weirong told state television in November 2009 that Chinas fourth-generation fighter, a reference to stealth technology, would begin testing soon and could enter service in eight years. Analysis of the J-20 photos indicates it is larger than Russian or U.S. equivalents, probably letting it fly farther and carry heavier weapons, the reports said.