"Equipped with surface supplied air rigs, divers will access sealed compartments located in damaged parts of the ship" the fleet said in a statement announcing that divers had joined the search. "Additionally, they will conduct damage assessments of the hull and flooded areas."
The collision tore a gaping hole in the McCain's left rear hull and flooded adjacent compartments including crew berths and machinery and communication rooms. Five sailors were injured. The destroyer is now docked at Singapore's naval base.
It was the second major collision in two months involving the Pacific-based 7th Fleet and the Navy has ordered a broad investigation into its performance and readiness. Seven sailors died in June when the USS Fitzgerald and a container ship collided in waters off Japan.
Megan Partlow of Ohio, who says her fiancee was on board the McCain, told The Associated Press in a Facebook message that they last communicated on Sunday and she was losing hope of seeing him again.
"My last text to him was 'be safe', which is the same way we end every conversation. I'm just ready for answers," she said. The identities of the missing have not been disclosed but Partlow said her fiancee's parents were in touch with the Navy's family assistance center.
Navy Adm. John Richardson, the chief of naval operations, on Monday ordered a pause in 7th Fleet operations for the next couple of days to allow commanders to get together with leaders, sailors and command officials and identify any immediate steps that need to be taken to ensure safety.
A broader U.S. Navy review will look at the 7th Fleet's performance, including personnel, navigation capabilities, maintenance, equipment, surface warfare training, munitions, certifications and how sailors move through their careers. Richardson said the review will be conducted with the help of the Navy's office of the inspector general, the safety center and private companies that make equipment used by sailors.
The McCain had been heading to Singapore on a routine port visit after conducting a sensitive freedom-of-navigation operation last week by sailing near one of China's man-made islands in the South China Sea.
The guided-missile destroyer and the Alnic MC oil tanker collided about 4.5 nautical miles (8.3 kilometers) from Malaysia's coast at the start of a designated sea lane for ships sailing into the busy Singapore Strait.
There was no immediate explanation for the collision. Singapore, at the southern tip of the Malay Peninsula, is one of the world's busiest ports and a U.S. ally, with its naval base regularly visited by American warships.
The Singapore government said no crew were injured on the Liberian-flagged Alnic, which sustained damage to a compartment at the starboard, or right, side at the front of the ship some 7 meters (23 feet) above its waterline. The ship had a partial load of fuel oil, according to the Greek owner of the tanker, Stealth Maritime Corp. S.A., but no apparent spill.
Several safety violations were recorded for the oil tanker at its last port inspection in July, one fire safety deficiency and two safety-of-navigation problems. The official database for ports in Asia doesn't go into details and the problems apparently were not serious enough for the tanker to be detained.