The U.S. Navy unveiled a damning report Wednesday on collisions between two Japan-based destroyers and commercial vessels in the western Pacific that left 17 crew dead this summer, calling the accidents "avoidable" and faulting leadership shortcomings and an erosion of sailors' basic standards.

The Yokosuka, Kanagawa Prefecture-based USS Fitzgerald, a guided-missile destroyer, collided with a container ship in the waters south of Tokyo Bay in June, killing seven sailors, while the USS John S. McCain, a destroyer also based at Yokosuka, smashed into an oil tanker as it approached Singapore just over two months later, leaving 10 of its crew dead.

The navy's first official report into the causes of the collisions revealed that both occurred in the wake of failures by officers and sailors on the bridge and raises troubling questions about the basic abilities of the Yokosuka-based 7th Fleet and the navy's surface fleet.