The decision to remove Aucoin from the post in Japan came as the US Navy undertakes a fleet-wide global investigation after Monday’s incident involving the USS John S. McCain, which left 10 sailors missing and five injured.

The 7th Fleet, which compromises ships, submarines and aircraft, is the centrepiece of the US military presence in Asia, undertaking sensitive missions such as operations in the South China Sea and around the Korean peninsula.

Aucoin has been commander of the fleet since September 2015 and has been in the navy since 1980. The Navy said Rear Admiral Phil Sawyer, who had already been named to succeed Aucoin earlier, will assume command immediately.

The McCain had 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, sparking a furious response from Beijing.

The déjà vu collision with an oil tanker was the US Navy’s fourth serious incident in the western Pacific this year, and mirrored a similar disaster in June that claimed the lives of seven sailors off the coast of Japan.

In January, the USS Antietam ran aground near Yokosuka, Japan, where the US 7th Fleet is based. In May, the USS Lake Champlain ran into a South Korean fishing vessel. And just last week, the Navy relieved the commander of the USS Fitzgerald, a guided missile destroyer that on June 17 was hit by a container ship, with deadly consequences.

Now, with 10 sailors presumed dead near the Strait of Malacca following the McCain’s mishap, the question of what, if anything, these accidents have in common has become front-of-mind.

One distinct possibility is a fleet that’s stretched too thin, forced to combine training with deployments over a vast area teeming with US strategic interests, according to two retired US Navy officers.

In a video posted on Twitter, the chief of naval operations, Admiral John Richardson, said he has directed “a more comprehensive review to ensure that we get at the contributing factors, the root causes of these incidents.”

From 1998 to 2015, the US Navy shrank by 20 per cent, to 271 ships, while the number of vessels deployed overseas remained at about 100 ships, Bryan Clark, a senior fellow at the Centre for Strategic and Budgetary Assessment, wrote in a 2015 article for The National Interest. Clark concluded that each ship has to work 20 per cent more to meet demand.

The current fleet size doesn’t properly support the demand for 85 ships to 105 ships deployed to sea at any given moment – the average for the past 50 years – said retired US Navy captain Jerry Hendrix, who also served as director of naval history and is now a senior director at the Centre for a New American Security.

“When you’re trying to keep that many out to sea ... something’s got to give,” he said. “The bucket that gets taken away from is training. I think the training has begun to break down in the fleet.”

Bryan McGrath, a retired US Navy captain who commanded a destroyer similar to the McCain, the USS Bulkeley, said that what “we’re seeing is a fraying Navy, especially over in the western Pacific.” The cold war’s end led to a navy-wide diminution of “basic war-fighting skills,” he said.

“We won the war and as a result, we took a big deep breath, and now we are recovering from that breath,” said McGrath, an analyst with defence consultancy FerryBridge Group LLC.

“Having these two ships taken out of action has a real tactical impact”

The ships are two of the US Navy’s most advanced, most manoeuvrable Arleigh Burke-class destroyers, which were first commissioned in 1991 and constitute the core of the service’s surface warfare capability.

Watch: USS John S. McCain at Singapore naval base

The US Navy’s overall fleet size, currently at 276 ships, is inadequate, given the size of its workload, Hendrix and McGrath said. In December, the US Navy laid out an aspirational benchmark, seeking a 355-ship fleet as part of its “Force Structure Assessment.

That number of vessels is “the level that balanced an acceptable level of war-fighting risk to our equipment and personnel against available resources and achieves a force size that can reasonably achieve success,” the US Navy said in the report.

The US Navy “has overemphasised resources used to incrementally increase total ship numbers at the expense of critically needed investments in areas where our adversaries are not standing still, such as strike, ship survivability, electronic warfare and other capabilities,” Obama administration Defence Secretary Ash Carter wrote in a memo to the US Navy in 2015.

But for now, the temporary loss of the McCain and the Fitzgerald has made a complex playing field more difficult to manage.

“This nation has global responsibilities and global interests,” McGrath said. “And when you have two emerging competitors in China and Russia, and then two other threats in Iran and North Korea, that makes for a very, very busy Navy.”

One, he added, that is “thinly stretched”.

Agence France-Presse, Bloomberg