There should have been lookouts on watch on the port, starboard and stern of the destroyer Fitzgerald — sailors scanning the horizon with binoculars and reporting by headsets to the destroyer’s bridge. At 1:30 a.m. last Saturday, off the coast of Japan south of Tokyo, they could hardly have failed to see the 730-foot freighter ACX Crystal, stacked with more than 1,000 containers, as it closed in.

Radar officers working both on the bridge and in the combat information center below it should have spotted the freighter’s image on their screens, drawing steadily closer. And under standard protocol, the Fitzgerald’s captain, Cmdr. Bryce Benson, should have been awakened and summoned to the bridge to assure a safe passage long before the ships could come near each other.

But none of that happened. The Fitzgerald’s routine cruise in good weather through familiar, if crowded, seas ended in the most lethal Navy accident in years. Seven sailors lost their lives.

As investigators try to figure out what many veteran seamen describe as an incomprehensible collision, they have plenty of mysteries to unravel. In addition to the questions for the destroyer’s crew, there is the peculiar course of the Crystal after the accident, recorded by ship-tracking websites. It raises the possibility that no one was awake, or at least aware of their surroundings, when the two ships hit.