Washington (CNN)The US Navy has released a report concluding that two fatal collisions that resulted in the deaths of 17 sailors during the summer were "avoidable." The guided-missile destroyers USS Fitzgerald and USS John S. McCain collided with commercial ships in June and August, respectively. In both collisions, the Navy found numerous failures by the crews and commanders of the ships. Those failures included not following standard navigation and seamanship practices, and poor situational awareness of what the ships were facing as they navigated congested seas off Japan and Singapore.