Singapore's transport ministry, releasing the results of its investigation into the incident, said a "series of missteps" by the destroyer's crew and insufficient action by those of the tanker, the Alnic MC, contributed to the accident.
The vessels smashed into each other in the predawn hours of August 21, 2017 in the busy shipping lanes around the Strait of Malacca. There were no casualties among the tanker's crew.
The commander of the John S. McCain is facing charges including negligent homicide and dereliction of duty, the US Navy said in January, after its own investigation into the incident found "multiple failures" by the ship's crew.
Singapore said its 35-page report did not blame any organisation or individual for the fatal crash, but found the warship made an abrupt turn after a transfer of controls caused confusion among the crew.
"The collision... happened because of a sudden turn to port (left) by JSM (John S. McCain), which caused it to head into the path of the (tanker)," the report said.
It also noted that several sailors on watch at the John S. McCain during the collision had been assigned from another warship with steering control systems that were "significantly different".
"These differences were not compensated for. Inadequacies in training and familiarisation before the task allocation may have contributed to the actions on John S. McCain," it said.
The collision took place within three minutes of the warship's sudden turn, it said, adding however that the actions taken by the tanker's crew "were insufficient to avoid" the smashup.
"When the bridge team of Alnic MC saw the USS John S. McCain turning, it presumed that the (warship) would be able to safely pass ahead," it said.
The incident came after another destroyer, the USS Fitzgerald, smashed into a Philippine-flagged cargo ship off Japan in June 2017, leaving seven sailors dead.
In a report on the two separate collisions, US Chief of Naval Operations Admiral John Richardson said both were "preventable and the respective investigations found multiple failures by watch standers that contributed to the incidents".
The US Navy said in November that the John S. McCain collision "resulted primarily from complacency, over-confidence and lack of procedural compliance".
"In particular, McCain's commanding officer disregarded recommendations from his executive officer, navigator and senior watch officer to set sea and anchor watch teams in a timely fashion," it said.//AFP