U.S. navy destroyer USS Fitzgerald sailed back to its base in Yokosuka, with seven of its sailors still missing after it collided with a Philippine-registered container ship more than three times its size in eastern Japan this morning.

The Fitzgerald, an aegis guided missile destroyer, collided with the merchant vessel, some 56 nautical miles southwest of Yokosuka.

The Navy said the ship was able to operate under its own power with limited propulsion. The Japanese coast guard said separately the Fitzgerald was towed back to Yokosuka by a tugboat at about 3 knots.

Three aboard the destroyer had been medically evacuated to the U.S. Naval hospital in Yokosuka, including the ship’s commanding officer.

Search and rescue efforts by U.S. and Japanese Aircraft and surface vessels were continuing for the seven missing sailors.