The search continues for seven U.S. Navy sailors still unaccounted for after the destroyer USS Fitzgerald collided with a merchant vessel off the coast of Japan early Saturday morning local time, causing massive damage and flooding spaces aboard the ship, the Navy said.

Three other crew members, including the ship's commanding officer Cmdr. Bryce Benson, were medically evacuated and are now awake and under observation at U.S. Naval Hospital Yokosuka. The ship returned to its homeport of Yokosuka this morning Washington time, 16 hours after the collision.

Fitzgerald collided with the Philippine-flagged merchant vessel ACX Crystal, which is about four times the size of the destroyer, about 56 nautical miles southwest of Yokosuka at 2:30 a.m. local time. The collision tore into the starboard side of the destroyer's superstructure above and below the waterline, and sailors spent hours fighting flooding in two berthing compartments, a machinery space and radio room, the Navy said.

"While those efforts helped stabilize the flooding, it remains uncertain how long it will take to gain access to the spaces once the ship is pier side in Yokosuka in order to methodically continue the search for the missing," according to a statement from the Navy's 7th Fleet.

Back at sea, the Japanese Coast Guard is leading the search for the missing sailors, along with the destroyer USS Dewey, a U.S. Navy P-8 Poseidon maritime patrol aircraft, and Japanese navy ships, helicopters and a P-3 Orion surveillance plane.

Vice Adm. Joseph Aucoin, 7th Fleet commander, was at the pier to greet the ship along with family members. "This has been a difficult day," Aucoin said. "I am humbled by the bravery and tenacity of the Fitzgerald crew. Now that the ship is in Yokosuka, I ask that you help the families by maintaining their privacy as we continue the search for our shipmates."

"I want to highlight the extraordinary courage of the Fitzgerald Sailors who contained the flooding, stabilized the ship, and sailed her back to Yokosuka despite the exceptionally trying circumstances," said Rear Adm. Charles Williams, Task Force 70 commander.