A sailor from the aircraft carrier USS Theodore Roosevelt, who has been missing since Dec. 10, has been declared dead, Navy officials announced.

Search and rescue efforts ended on Dec. 12 after failing to locate the sailor, according to U.S. 3rd Fleet.

“The loss of our sailor is felt deeply by all on board,” Capt. Eric Anduze, the Theodore Roosevelt’s commanding officer, said in a statement. “The entire Theodore Roosevelt team sends our deepest condolences to the family of our missing shipmate.”

During more than 55 hours, the Theodore Roosevelt along with other Navy and Coast Guard ships and aircraft searched more than 607 square nautical miles for the sailor, whose name has not been officially released by the Navy, a 3rd Fleet news release says.

The search began on Dec. 10 after one of the aircraft carrier’s lookouts spotted what appeared to be a person in the water. A command-wide muster revealed that one of the ship’s sailors was unaccounted for.

The Theodore Roosevelt got underway early last week and is currently in the eastern Pacific.

Investigators are looking into how the sailor went overboard, the 3rd Fleet news release says.

“The Carrier Strike Group Nine team sends our thoughts and prayers to the family and loved ones of our missing shipmate,” said Rear Adm. Doug Verissimo, commander of Carrier Strike Group Nine, in a statement. “I offer my thanks to all the sailors and Coast Guardsmen who were involved in the search.”