BANGKOK >> One major U.S. Navy collision may be an accident. Twice in two months could be a coincidence. Or it could point to a bigger failing in how the U.S. navigates its warships around the world.

It is unclear how the collision occurred early Monday between the USS John S. McCain and a Liberian-flagged oil tanker in a crowded shipping lane off Singapore, leaving 10 American sailors missing and five injured.

The broken destroyer, now docked in Singapore while investigators look into the cause of the crash, is the fourth Navy vessel involved in an accident this year in the Pacific. No one was hurt in the first two incidents, but seven Navy sailors were killed in June in a collision between the USS Fitzgerald and a container ship off the coast of Japan.

“While each of these four incidents is unique, they cannot be viewed in isolation,” said Adm. Scott Swift, commander of the U.S. Pacific Fleet.

Analysts said the two latest accidents are especially sobering, especially at a moment when U.S. warships occasionally patrol the disputed South China Sea to the consternation of Beijing, and President Donald Trump has swapped threats with North Korea’s leader, putting nations across Asia on edge.

“It is truly extraordinary, not only that it should happen, and not only that it should happen to the U.S. Navy, but that it should happen repeatedly within weeks in the same geographic area,” said John Blaxland, head of the Strategic and Defence Studies Center at the Australian National University in Sydney.

Long-standing protocols for avoiding collisions include having sailors watching the water on all sides, radar systems detecting obstructions and commanders carving clear paths ahead.

The Navy has ordered an “operational pause,” which Blaxland said makes sense “to explore what on Earth is happening.”

Though the investigation into the McCain collision has only just begun, analysts say there are many possible causes, including crew fatigue, command shortfallings, radar malfunctions, software glitches and even jammed signals that might have prevented the warship from detecting obstacles.

Both the McCain and the Fitzgerald are guided-missile destroyers stationed with the U.S. Navy’s 7th Fleet in the Pacific. Both collisions occurred in early-morning darkness in crowded shipping lanes, near allied shores. And both were struck by enormous commercial vessels that would have been slower to change course to avoid impact.

Both warships sustained damage that caused flooding in several internal compartments including sleeping berths.

“The U.S. Navy has been conducting a lot of activities across the South Pacific region, and it brings up the question of whether the force is stretched, covering so many areas,” said Ridzwan Rahmat, a naval defense expert for Jane’s. “There is a question of possible crew fatigue. That is the question I would be asking as an investigator, is this tempo of operations sustainable?”

The McCain had been sailing to a routine port visit in Singapore via a narrow, rocky strait that is among the world’s busiest. Some 1,000 ships are in the strait at any given time, guided by a system of traffic lanes.

Though ships have been plying the congested area for decades with few incidents, the accident rate in the region is rising, according to insurer Allianz Global Corporate & Specialty. While Southeast Asia accounted for 21 percent of global shipping losses registered in 2007-2015, that rose to 27 percent in 2016, it said.

The Fitzgerald had been further north, also in a busy shipping lane that is a gateway to Tokyo. It had been returning from several days of bilateral exercises to its port in Japan on June 17 when the bow of the ACX Crystal container ship slammed into its right side, quickly flooding several areas inside, including a berthing area where 35 sailors were asleep.

In a statement last week, the 7th Fleet said the June 17 collision “was avoidable, and both ships demonstrated poor seamanship.” The ship’s captain has been relieved of duty and more than a dozen other sailors punished, though some of the crew were commended for helping to save fellow crew members after the collision.

Navy officials continue to investigate the Fitzgerald collision, and analysts said the McCain accident may cause them to examine it further still.

“This second incident may imply an underlying issue in the Navy’s command culture,” said Andrew Lambert, a professor of naval history at Kings College London. “Being the biggest and the best for decades can breed complacency, which is not a good thing at sea.”

In both collisions, no data on the warships’ movements are publicly available. In a common security practice by U.S. Navy commanders, neither had switched on their Automated Identification Systems, which involve radio transponders to help prevent such collisions.

They should have had their own radar systems on — a usually failsafe way to detect nearby obstacles. Yet, both collisions involved large commercial ships with massive radar profiles that are “impossible to miss, if you are looking,” Lambert said.

“There’s really only two ways you can fail to avoid ships of that size — one is not to have the radar switched on; the other is not to be looking at the radar.”

The U.S. Navy said the McCain sustained damage to its port side aft, or left rear, while the Alnic MC commercial tanker sustained damage at the front. That is not enough information to suggest fault or cause.

A month before the Fitzgerald’s accident, a South Korean fishing boat collided with the USS Lake Champlain guided-missile cruiser off the Korean Peninsula while it was operating in the western Pacific as part of the 3rd Fleet’s USS Carl Vinson aircraft carrier strike group. No one was injured in the May 9 mishap.

On Jan. 31, the USS Antietam guided-missile cruiser ran aground near the Yokosuka base that is the home port for the 7th Fleet, damaging its propellers and leaking about 1,100 gallons of hydraulic fuel into Tokyo Bay. The ship’s commander was relieved from duty.

Blaxland, the Australian defense expert, said the repeated incidents have been shuddering in terms of the Navy’s confidence.

“The U.S. Navy has a reputation for being peerless. It is the gold standard by which other nations measure themselves,” Blaxland said. “There’s no doubt it has hurt the Navy’s reputation. The question is how quickly can they get to the bottom of it.”