A fatal collision between a U.S. destroyer and a Philippine container ship off the Izu Peninsula in 2017 was caused by U.S. crewmen failing to follow lookout protocols, Japan's transport safety authorities concluded Thursday.

A report by the Japan Transport Safety Board said the watch team on the USS Fitzgerald was unable to figure out the intentions or actions of the ACX Crystal because it was concentrating on another vessel in the vicinity. Additionally, radar information about the Philippine ship was incomplete.

In compiling the report, Japanese authorities were not allowed to directly interview any crew members of the U.S. Navy ship. Seven American sailors were killed and three others on the destroyer, including the captain, were injured.