The incident took place in the South China Sea, in international waters about 75 miles south of Hainan Island.
The Defense Department said the following:
"On March 8, 2009, five Chinese vessels shadowed and aggressively maneuvered in dangerously close proximity to USNS Impeccable, in an apparent coordinated effort to harass the U.S. ocean surveillance ship while it was conducting routine operations in international waters.
"The Chinese vessels surrounded USNS Impeccable, two of them closing to within 50 feet, waving Chinese flags and telling Impeccable to leave the area.
"Because the vessels' intentions were not known, Impeccable sprayed its fire hoses at one of the vessels in order to protect itself. The Chinese crew members disrobed to their underwear and continued closing to within 25 feet."
A protest has already been lodged with the Chinese government and it was to be repeated face-to-face to a Beijing military attache at a Pentagon meeting Monday, according to officials.
Of course, China considers most of the South China Sea as its own, which has led in the past to sovereignty issues with other countries in the region.