Returning from a nine-month deployment to the Persian Gulf, Capt. Russell Tjepkema said, "This 24-hour period was the hardest 24-hour period of the entire deployment."
The Nassau is carrying the 24th Marine Expeditionary Unit back to Camp Lejeune, North Carolina.
Dwayne Williams, a 23-year old petty officer third class from Philadelphia, Pennsylvania, was chasing a football Friday morning when he tripped and fell over the side of the ship, plunging 70 feet into the Atlantic, Tjepkema said.
The Nassau was about 900 miles [1,440 kilometers] off the Virginia coast, traveling about 18 knots [20.7 mph].
It was a clear day, and Williams could be seen waving his arms in the water, the captain said. Crew members threw him a float coat to help him stay buoyant and a smoke float, which allows someone lost at sea to send smoke signals, Tjepkema said.
Within five minutes of the fall, Tjepkema said, a rescue boat left the ship; within 10 minutes, a helicopter arrived to take part in the search; and within an hour, four more helicopters were on the scene.
The football, coat and smoke float were all found near where Williams had fallen over, but there was no sign of him.
Williams had not been wearing a life preserver onboard, and he was wearing coveralls and boots, which would weigh him down in the water, Tjepkema said.
Given the water's temperature, the life expectancy for someone stuck in that part of the Atlantic is 2 1/2 hours, he said. After that, "we knew we were looking for remains.
"There was no way I was going to leave that man there," he added.
Officers and crew searched for nine hours, until it became too dark to keep trying, he said.
As the ship resumed its journey Saturday to North Carolina, Tjepkema said, "My mind says this is the right thing to do, but my heart tells me to go back and look for the guy."
Williams' wife and mother have been told, and are en route to North Carolina, where they will meet his unit, Tjepkema said, adding that the petty officer had no children.
The crew, Tjepkema said, is shaken "to the very core." The ship held a memorial service Saturday morning.
The USS Nassau is expected to arrive in North Carolina on Monday morning, offload the troops and equipment, and continue to its home port of Norfolk, Virginia.