These sailors died in the collision of the USS Fitzgerald and Philippine-flagged merchant vessel on June 17, 2017.

The back-to-back collisions of two US Navy warships with commercial vessels this summer, which killed 17 US sailors, were the result of a series of preventable errors by those on board, according to a Navy investigation released on Wednesday.

The crews failed to follow navigation and basic naval safety procedures, the report says.

"Both of these accidents were preventable, and the respective investigations found multiple failures by watch standers that contributed to the incidents,” said Adm. John Richardson, the US Navy’s chief of naval operations. "We must do better."

The two collisions followed two previous incidents in Asian waters this year. The 17 deaths were greater that the 12 US military members killed so far this year in Afghanistan.

The USS Fitzgerald, a guided missile destroyer, was rammed by a Philippine merchant vessel on June 17 off the coast of Japan. The bodies of seven US sailors were recovered in flooded berthing compartments a day later. Three more sailors were injured, including Cmdr. Bryce Benson, the ship’s commanding officer. Sailors had to use a sledgehammer to break through the door into Benson’s cabin, where he'd been sleeping, and found him “hanging from the side of the ship,” the report says.

Two months later, on Aug. 21, the USS John S. McCain collided with an oil tanker in waters east of Singapore, along one of the world’s most congested shipping routes. Divers recovered the bodies of 10 sailors in the days after the accident.

The investigation found that the Fitzgerald’s watch teams “disregarded established norms of basic contact management and, more importantly, leadership failed to adhere to well-established protocols put in place to prevent collisions.” Crew members mistakenly calculated that the other ship would pass them from a 1,500- yard distance and did not slow their speed, failing to correct course until it was too late.