A Navy helicopter doing training operations from a ship crashed 50 miles (80 kilometers) off the California coast, killing one crew member and leaving three others missing long after darkness fell over the Pacific.
One sailor died Friday after being pulled alive from the water, the Navy said.
A search-and-rescue operation was under way to locate the others, said Navy spokesman Cmdr. Jack Hanzlik.
"It's a sad time whenever we lose shipmates like this, so our hearts and prayers go out to the families," he said.