The Navy has found that two ship collisions that combined to kill 17 sailors at sea were preventable and caused in part by “multiple failures” by servicemembers who were standing watch the nights of the incidents, the service said Wednesday.

The USS Fitzgerald and the USS John S. McCain, both guided-missile destroyers, suffered catastrophic collisions June 17 and Aug. 21, respectively. The Fitzgerald accident killed seven sailors off the southern coast of Japan, while the McCain collision killed 10 sailors near Singapore.

Adm. John Richardson, the chief of naval operations, said Wednesday in a statement upon releasing the investigation results that the service must do better.

“We are a Navy that learns from mistakes and the Navy is firmly committed to doing everything possible to prevent an accident like this from happening again,” Richardson said. “We must never allow an accident like this to take the lives of such magnificent young Sailors and inflict such painful grief on their families and the nation.”

The Fitzgerald collision was attributed to its watch teams disregarding established ways of contacting other ships and safety precautions put in place.

The ship’s captain, Cmdr. Bryce Benson, executive officer, Cmdr. Sean Babbitt, and senior enlisted sailor, Command Master Chief Brice Baldwin, all were absent from the ship’s bridge at the time of the crash, “during an evolution where their experience, guidance and example would have greatly benefited the ship,” the Navy found. They were removed from their jobs in August.

The McCain collision “resulted primarily from complacency, overconfidence and lack of procedural compliance,” the Navy found, and occurred two months after the Fitzgerald collision created uproar in the service. A major contributing factor was substandard knowledge of how to operate the ship’s control console.

“With regard to procedures, no one on the Bridge watch team, to include the commanding officer and executive officer, were properly trained on how to correctly operate the ship control console during a steering casualty,” the investigation found.

The McCain’s captain, Cmdr. Alfredo Sanchez, and executive officer, Cmdr. Jessie Sanchez, were removed from their positions last month.