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 service members 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 required safety precautions that were in place. The investigation found that at about 11 p.m. on June 16, the ship’s top two officers — Cmdr. Bryce Benson, the ship’s captain, and Cmdr. Sean Babbitt, the ship’s executive officer, left the ship’s bridge for the evening.By 1 a.m., the Fitzgerald was moving past Japan’s Oshima Island, and approached three merchant ships from the starboard, or right, side of the ship. There was "minimal" distance between the Fitzgerald and the other vessels, and all three presented a collision hazard, the investigation found.The Navy determined that the Fitzgerald was in a crossing situation with each vessel, meaning it was the sailors’ obligations to take maneuvering action to avoid them. But in the 30 minutes leading up to the collision, neither the Fitzgerald nor the much larger MV ACX Crystal, a Philippine-flagged container ship, did so until just a minute prior to the disaster.The investigation faulted the officer of the deck, who was not named in the documents, for failing to maneuver as needed, sound the danger alarm on the ship, contact the Crystal or call his own captain, as required."Initially, the Officer of the Deck intended to take no action, mistaking CRYSTAL to be another of the two vessels with a greater closest point of approach," the investigation found. "Eventually, the Officer of the Deck realized that FITZGERALD was on a collision course with CRYSTAL, but this recognition was too late."Benson, Babbitt and the senior enlisted sailor of the ship, Command Master Chief Brice Baldwin, were cited for being absent from the 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.In the McCain collision, the ship’s captain, Cmdr. Alfredo Sanchez, and executive officer, Cmdr. Jessie Sanchez, were on the bridge, but confusion about how the ship’s steering work caused chaos.The investigation found that it was about 5:19 a.m. on Aug. 21 when the ship’s captain noticed that the ship’s helmsman, who was steering the vessel, was having difficulty maintaining course while in a congested ship corridor. In response, the captain put a second sailor in charge of shifting speed control while keeping the steering with the helmsman. The decision prompted confusion, with the sailors thinking that steering also had been transferred to the second sailor even though it had not.The helmsman reported a loss of steering, prompting the commanding officer to order the ship’s speed from 10 knots to five knots. But the second sailor reduced the speed only on one the ship’s rear shaft, steering it toward the Alnic MC, a much larger oil tanker."Although JOHN S MCCAIN was now on a course to collide with ALNIC, the Commanding Officer and others on the ship’s bridge lost situational awareness," the investigation recounted. "No one on the bridge clearly understood the forces acting on the ship, nor did they understand the ALNIC’s course and speed relative to JOHN S MCCAIN during the confusion."Three minutes after the steering problems were reported, the McCain’s crew regained control. But it was too late, and the ships collided at 5:24 a.m."The collision was felt throughout the ship," the investigation report said. "Watchstanders on the bridge were jolted from their stations momentarily and watchstanders in aft steering were thrown off their feet. Several suffered minor injuries. Some Sailors thought the ship had run aground, while others were concerned that they had been attacked. Sailors in parts of the ship away from the impact point compared it to an earthquake. Those nearest the impact point described it as like an explosion."The investigation found that the McCain collision "resulted primarily from complacency, overconfidence and lack of procedural compliance." It added that "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 two senior officers were removed from their positions last month.