Multiple investigations have yet to apportion blame for the accident that killed seven U.S. sailors aboard the guided missile destroyer the USS Fitzgerald.

However, the punishments are the first public admission by the U.S. Navy that mistakes by the crew contributed to the deadliest incident on a U.S. warship since Islamist extremists bombed the USS Cole in Yemen's Aden harbor in 2000.

"The collision was avoidable and both ships demonstrated poor seamanship. Within Fitzgerald, flawed watch stander teamwork and inadequate leadership contributed to the collision," the U.S. Seventh Fleet said in a media release.

In the first detailed account from one of those directly involved in the collision in the early hours of June 17, the captain of the cargo ship the ACX Crystal said in a report seen by Reuters his crew signaled the Fitzgerald with flashing lights around 10 minutes before the collision. The Fitzgerald did not respond or alter course, it said..