WASHINGTON - Monday's collision between Aegis-equipped destroyer USS John S. McCain and an oil tanker - the fourth major accident in the US Pacific fleet this year - prompted a fleet-wide investigation and plans for temporary halts in operations to focus on safety.
The destroyer was damaged near the rear on its port, or left-hand, side. Sources told The Straits Times that three bodies out of the 10 missing sailors have been found and are awaiting identification. Five others were injured, none with life-threatening conditions.
The most significant of the recent ship accidents occurred in June when another Navy destroyer, the USS Fitzgerald, collided with a freighter off Japan, killing seven U.S. sailors. The collision caused significant damage to the Fitzgerald above and below the waterline, flooding berths, a machinery area and the radio room.
The two most recent collisions of US Navy vessels with large commercial vessels have caught the international shipping community by surprise.
Deadly collisions among large commercial ships have become extremely rare, even though large freighters and tankers vastly outnumber naval vessels on the high seas.
Below are some of the most asked questions on what caused the collision.
1. Was the accident caused by human or technical error?
An initial review by the navy of the June collision of the destroyer USS Fitzgerald off the coast of Japan suggested multiple personnel failures.
To its credit, the service moved quickly to discipline a dozen sailors, including the two top officers and the top enlisted sailor, even while the investigation of the incident continues.
Among other things, the Fitzgerald's commander was not on the bridge when the crash occurred, though protocol requires the captain's presence when other ships are passing nearby.
According to Allianz statistics, more than three-quarters of all maritime incidents are attributable to human error. Collisions usually involve a combination of factors such as malfunctioning equipment and a breakdown in communication among the ship's officers, said Captain Rahul Khanna, head of marine risk consulting at the global insurance company.
In USS McCain's case, a US Navy official told CNN the warship suffered a "steering failure" as the warship was beginning its approach into the Singapore Strait, causing it to collide with a commercial tanker Monday.
The official said it was unclear why the crew could not utilise the ship's backup steering systems to maintain control of ship.
Earlier, another US Navy official told CNN there were indications the destroyer experienced a loss of steering right before the collision, but steering had been regained after the collision.
Admiral Scott Swift, commander of US Pacific Fleet, on Tuesday said at a press conference in Singapore there was no indications of cyber attacks and interference in Monday's collision.
Remarks made by Admiral John Richardson,the Chief of Naval Operations, suggested a focus on "how we do business on the bridge".
2. Did darkness and heavy sea traffic make things worse?
Like the Fitzgerald, the McCain was travelling in a heavily trafficked sea lane in darkness when the collision occurred, making human error more likely.
The waters where the latest incident took place - the Singapore Strait, a 10-mile-wide maritime gantlet brimming with ships moving between the Indian Ocean and South China Sea - is a potential chokepoint and require heightened precaution.
Khanna told Washington Post the waters outside Singapore are particularly dense and hard to navigate, with a constant stream of ships waiting offshore to pick up loads and crisscrossing the passage after refuelling.
"It's a very dynamic environment. These are areas where lots of ships funnel through," said Khanna, who captained oil tankers for two years.
"It requires the utmost level of situational awareness to pass through, and every sailor is aware of that."
— Chief of Navy - PTL (@mykamarul) August 21, 2017
Ships often do not stay in designated traffic separation zones.
At night, many merchant ships light up their decks at night to ward off local pirates, but the bright lights can also dangerously obscure the vision of officers on approaching ships, reported New York Times.
Monday's collision took place at 0524hrs.
3. Were the crew well-trained to cope?
To deal with these challenges, extra sailors are assigned as lookouts and others are added below decks to help in case of steering or engine problems.
A ship's commanding officer, navigator or executive officer is often on the bridge during the traversal. Navigation teams routinely hold briefings before entering narrow waters to go over safety issues.
Radar operators and combat information officers also track ships.
"You need to be extra careful," Khanna said. "Your bridge team has to perform exceedingly well. They should be trained well enough to deal with this."
Admiral Richardson says the fleet-wide review will examine basic seamanship and teamwork.
A broader review of the 7th Fleet based in Japan would examine its pace of operations; readiness issues, including maintenance, equipment and personnel; and whether the fleet was properly training its officers and ship crews.
Three of the four naval vessels involved in mishaps since the beginning of this year are under the command of the 7th Fleet.
The US Navy's series of collisions this year, at a time of steadily improving overall shipping safety, suggests that the Navy may need to do more training of the officers on its bridges, said Captain Harry Bolton, director of marine programmes at California State University Maritime Academy in Vallejo.
"That's a lack of what we call bridge-team management," he told New York Times. "It's fixable: They bring the same kind of training that we get."
4. Was the US navy and personnel overstretched?
Analysts said the collisions raised questions about whether the US navy was overstretched in Asia as it seeks to combat Chinese assertiveness in the South China Sea and North Korea's nuclear ambitions, according to Agence France-Presse.
The McCain been heading for a routine stop in Singapore after carrying out a "freedom of navigation operation" in the disputed South China Sea earlier in August around the Mischief reef in the disputed Spratly Islands.
In a blog post on Tuesday (Aug 22), The National Interest said the fact that the US Navy is forcing its fleet to do more with fewer ships to perform its global mission might have contributed to the two most recent collisions.
"The U.S. combat fleet is already over-stretched," Seth Cropsey, director of the Center for American Seapower at the Hudson Institute told The National Interest.
Because the fleet is being pushed so hard, the Navy might be using its time at sea to train during operational deployments, Jerry Hendrix, director of the Defense Strategies and Assessments Program at the Center for a New American Security, told The National Interest.
"Something has to give, and right now, it's training," Hendrix said.
In a scathing editorial, China's Global Times said US warships patrol too frequently in the Asia-Pacific and that frequent collisions of US warships with merchant vessels was a warning to the Americans that they should restrain themselves.
But Adm Swift, in response to a question whether the collision reflected that the US naval personnel were overworked and understaffed, said: "I don't think that's the case. I was on John S. McCain, looking into the eyes of sailors. Even after the heroic efforts, I didn't see exhaustion."
5. Why did the oil tanker emerge relatively unscathed?
Compared to the McCain, the Liberian-flagged oil tanker Alnic MC sustained less damage. No crew on the tanker was hurt and there was no oil spill.
The New York Times reported that navy ships are unusually vulnerable if they become involved in collisions, and those vulnerabilities may explain why so many sailors have perished or disappeared in the two crashes this summer.
The crews of naval vessels have their sleeping berths near the waterline, so the berths may flood quickly after a collision.
By contrast, the crews of commercial vessels tend to sleep in cabins near the back, above the cargo and engines, and far above the water.
"The architecture of the ships is completely different," Basil M. Karatzas, a longtime New York ship broker, told New York Times.
Military designers have tried to keep the profiles of naval vessels as low as possible, to make them smaller targets for enemy guns, aircraft and missiles, and have avoided putting sleeping quarters high above the water.
Almost all tankers have double hulls, as do about a third of dry-bulk freighters, which carry cargos like corn and iron ore. These vessels have about a yard of space between the inner and outer hulls to act as a buffer during minor collisions, and this has made oil spills a rarity in recent years on the few occasions when tankers have brushed against other vessels.
Military vessels, however, seldom have such wide hollow spaces because they are designed to be sleek and fast.