mdsolar writes: Sixteen U.S. ships that participated in relief efforts after Japan's nuclear disaster five years ago remain contaminated with low levels of radiation from the crippled Fukushima Dai-ichi nuclear power plant, top Navy officials told Stars and Stripes. In all, 25 ships took part in Operation Tomadachi, the name given for the U.S. humanitarian aid operations after the magnitude-9.0 earthquake and subsequent tsunami on March 11, 2011. The tsunami, whose waves reached runup heights of 130 feet, crippled the Fukushima plant, causing a nuclear meltdown. In the years since the crisis, the ships have undergone cleanup efforts, the Navy said, and 13 Navy and three Military Sealift Command vessels still have some signs of contamination, mostly to ventilation systems, main engines and generators. "The low levels of radioactivity that remain are in normally inaccessible areas that are controlled in accordance with stringent procedures," the Navy said in an email to Stars and Stripes. "Work in these areas occurs mainly during major maintenance availabilities and requires workers to follow strict safety procedures."