A U.S. nuclear-powered submarine hit an unidentified object while submerged in the South China Sea, the U.S. Pacific Fleet announced Thursday. The collision, which happened Saturday, was severe enough to injure several sailors aboard the USS Connecticut. “The submarine remains in a safe and stable condition,” the U.S. Pacific Fleet said in a statement. “USS Connecticut’s nuclear propulsion plant and spaces were not affected and remain fully operational. The incident will be investigated.” The U.S. and its allies have been conducting military exercises in the region as China flies fleets of its planes close to Taiwanese airspace in a show of force.