Tokyo ? The U.S. Navy said that one of its nuclear-powered submarines had leaked minimally radioactive water earlier this year, threatening to cause a stir in Japan where both the U.S. military presence and its nuclear vessels are controversial.

The Navy said Friday it discovered the leak July 17 when a gallon of water spilled from a valve while the submarine was in dry dock for routine maintenance at Pearl Harbor in Hawaii. An investigation showed water may have been slowly leaking from the valve since March as the Los Angeles-class submarine traveled around the Pacific.