Google is offering a rare public glimpse of China's new ballistic-missile submarine, according to a researcher at the Federation of American Scientists.

"The new submarine was photographed by the commercial Quickbird satellite in late 2006 and the image is freely available on the Google Earth website," wrote Hans Kristensen on the Strategic Security Blog.

Kristensen identified the submarine, pictured alongside a naval pier, as a Jin-class vessel, one of five that China is expected to build.

Comparing the Google Earth image with a picture of China's existing Xia-class submarine, Kristensen was able to discern some of the features of the new submarine.

"The Jin-class appears to be approximately 35 feet (10 metres) longer than the Xia-class [submarine], primarily due to an extended mid-section of approximately 115 feet (35 metres) that houses the missile launch tubes and part of the reactor compartment," Kristensen wrote.

But the picture was not clear enough to resolve a debate over whether the Jin-class submarine has tubes for 12 or 16 nuclear-tipped missiles.

Discovery of the submarine image is likely to cause consternation within China's military, which generally keeps as low a profile as possible. If so, it wouldn't be the first time that Google Earth has caused worry inside China's government. In 2006, government officials reportedly expressed concerns over Google Earth imagery of the Zhongnanhai leadership compound in Beijing, an area normally off limits to prying public eyes.