The problem was complacency --that may be somewhat forgivable on the freighter's side, but not on the destroyer's side --it's a warship. It should always be on alert and at the ready. They should never be complacent. The captain allowed his sailors to become complacent.
I am hopeful the navy will not only examine this crew but will also examine the rest of the navy for laxness and failure to perform/dereliction of duties, etc.