– U.S. Navy ships worldwide will suspend operations for a day or two this week to examine basic seamanship and teamwork following the second collision of a Navy destroyer and larger commercial ship in two months, the country’s top naval officer said Monday.

Adm. John Richardson, chief of naval operations, said he had ordered two major actions after the collision between the destroyer USS John S. McCain and an oil tanker early Monday off the coast of Singapore that left 10 sailors missing and five injured.

First, Richardson said he had ordered an “operational pause” for Navy fleet commanders to review within the week teamwork, safety, seamanship and other “fundamentals.” During that time, commanders will suspend ship operations for a day or two. Second, the admiral said he had ordered a broader, monthslong review to examine the specific situation in the western Pacific, where the Navy has suffered four major ship accidents since February.

“That gives great cause for concern that there’s something out there that we’re not getting at,” Richardson told reporters at the Pentagon.

Off the Singapore coast, search teams scrambled Monday to determine the fate of the missing sailors from the McCain, a guided-missile destroyer that had been passing east of the Strait of Malacca en route to a port visit in Singapore.

At 5:24 a.m. local time, before dawn broke, the destroyer collided with the Alnic MC, a 600-foot vessel that transports oil and chemicals, the Navy said. The destroyer was damaged near the rear on its port, or left-hand, side.

More than half a day after the crash, 10 sailors on the ship remained unaccounted for. Five others were injured, none with life-threatening conditions, a Navy official said. Ships with the Singaporean and Malaysian navies and helicopters from the assault ship USS America were rushing to search for survivors.

Families of the ship’s crew members waited through the night in the United States, hoping for news of their loved ones.

“No word yet but some sailors have called on cell to families,” wrote Marla Meriano, the mother of Meghan Meriano, a 24-year-old electrical officer, in a Facebook post. “Thank you for all the prayers and remarks,” she wrote two hours later. “God has his plan and we serve him.”

The collision occurred in one of the world’s busiest shipping lanes, a narrow waterway of strategic significance connecting the Indian Ocean with the South China Sea, where Beijing has been challenging U.S. naval dominance. It immediately raised questions about the training and safety record of Navy ships, coming just two months after another Navy destroyer, the USS Fitzgerald, collided with a freighter off Japan, killing seven American sailors.

“Clearly this is an annus horribilis for the U.S. Navy,” said Euan Graham, director of the International Security Program at the Lowy Institute in Sydney.

Kirk Patterson, a former dean of the Japan campus of Temple University who has crossed the Pacific in a sailboat and circumnavigated Japan, said the collision was “really hard to understand with all the technology that’s out there in the world on a boat, especially a naval destroyer that’s supposed to be the best in the world.”

For a destroyer to be hit by an oil tanker would be “like an F1 sports car and a garbage truck,” he said. “Which one is going to be able to avoid the collision? An F1 racing car equipped with state-of-the-art missiles.”

A destroyer going through a difficult a passage like the Strait of Malacca would typically have half a dozen sailors, including two officers, on the bridge watching for the lights of other ships, said retired Navy Capt. Bernard D. Cole, an adjunct professor at Georgetown University and professor emeritus at the National War College.

In such clogged traffic, it would also be common for the commanding officer or the executive officer, the two most senior officers on board, to be on the bridge, he said. There would also be a navigator and other enlisted men in the combat information center scanning radar.

Once the oil tanker was detected, Cole said, the officer on deck or the commanding officer would propose some kind of evasive action to avoid the collision. But “in some places like the approaches to the Malacca Strait, geographically you don’t have a lot of flexibility.”

A picture of the McCain showed a gaping hole in its side right at the waterline, but the ship did not appear to be listing.

In a statement, the Navy said the destroyer had reached Changi Naval Base in Singapore. “Significant damage to the hull resulted in flooding to nearby compartments, including crew berthing, machinery and communications rooms,” the statement said. “Damage control efforts by the crew halted further flooding.”

Navy ships “frequently transit” the strait without incident, said Cmdr. Clay Doss, a spokesman for the 7th Fleet, with which the McCain is deployed. “It’s not unusual at all,” he said.

Yet Bonji Ohara, a research fellow at the Sasakawa Peace Foundation in Tokyo, said that one recurring problem was that while naval ships tended to have live crews on watch, most commercial ships work on autopilot mode to reduce costs, which can lead to problems in busy sea lanes.

While Graham said it “beggared belief” that any merchant vessel approaching the Strait of Malacca would be operating on autopilot, he acknowledged that “years of cost-cutting within the industry can mean that ships have skeleton crews that will be at their lowest level of watchfulness in the hours just before dawn.”

For the McCain to collide with the Alnic MC, a handful of separate functions in the safety chain, such as binocular sightings by officers in the observation deck and radar operations in the bridge and below, must have failed, according to a senior Navy officer.

While on operations, warships do not emit standard satellite tracking signals that other larger vessels use to avoid collision. “They don’t want other countries to know where they are going,” Graham said. “There is a degree of stealth. So that puts the balance of responsibility on the warship to maintain watchfulness in case it’s not spotted by other vessels.”

Commercial tankers can be reluctant to shift their course because maneuvering requires turning off the autopilot and costs time and money, the Navy officer added.

The Alnic MC, which has a gross tonnage roughly three times that of the McCain, is registered under a Liberian flag and was built in 2008, according to a marine registry. The tanker, which is now anchored in Singapore for damage assessment, was struck on the front part of its hull, but none of its crew were injured, according to a statement from the Maritime and Port Authority of Singapore. No oil leaks have been reported in the area, according to the Singaporean authority.

The Strait of Malacca is a strategic choke point between the Indian and Pacific oceans. Much of Asia’s oil imports transit through the channel and into the South China Sea.

President Donald Trump, asked about the collision by reporters at the White House on Sunday night, said, “That’s too bad.” He later offered his “thoughts & prayers” on Twitter to the sailors aboard the ship.

The collision on Monday came two months after one of the Navy’s deadliest accidents in years, when the Fitzgerald collided with a freighter off Japan. Seven people on the Fitzgerald were killed, and the Navy relieved the destroyer’s two top officers of their duties on Friday after an investigation into the collision. Both of the destroyer’s top commanding officers were asleep when the collision occurred.

In May, the USS Lake Champlain, a Navy guided-missile cruiser, collided with a South Korean fishing vessel, but no injuries resulted from that crash. In February, another such cruiser, the USS Antietam, ran aground in Tokyo Bay, gushing more than 1,000 gallons of hydraulic fluid near the U.S. naval base at Yokosuka, Japan.

The McCain, the Antietam and the Fitzgerald are all in the 7th Fleet and are based in Yokosuka. The ship involved in the collision on Monday is named after John S. McCain Sr., a Navy admiral during World War II, and his son, John S. McCain Jr., a Navy admiral in the Vietnam era. They are the grandfather and father of Sen. John McCain, R-Ariz., who offered his prayers for the crew.