My guess as to what happened is that there were initially two tankers in the picture (fact) and that the other tanker (the Wan Hai, I believe) was the perceived threat to the Fitzgerald. In avoiding the Wan Hai, the crew of the Fitzgerald set a course across the bow of the second tanker, the Crystal, which went undetected by the bridge until the collision, or was detected so close to the time of the collision that they couldn’t take action to avoid it.
It’s also possible that someone on board relayed the existence of the Crystal and the approaching threat but their message was interpreted as referring to the Wan Hai, which the Fitzgerald was already avoiding. This is speculation, of course, but the potential role of the Wan Hai has gotten little notice and is, I think, worth considering.
Something similar happened to the Porter years ago. It was in the process of avoiding one tanker when it was surprised by the existence of a second one, and collided with it.
I had not heard of other ships in the vicinity, but a third ship in the mix would definitely complicate matters. It wouldn't remove blame, but would at least explain that the situation was more complex than many know.
Still, if the tactical situation was that tenuous, the OOD should've had strict standing orders from the Captain to wake him immediately, and should have done so. Ship collisions in the open sea don't happen quickly; the situations that lead to them evolve over time, even dozens of minutes. The OOD (and bridge and CIC crews) should've recognized the potential for a dangerous encounter, and the OOD should've taken the ship out of harm's way.
What I want to know is, what was the dialog on the bridge between the OOD (possibly JOOD), quartermaster of the watch and the lookouts? Also, what was CIC telling the bridge? Did anyone identify a close-in CPA? Did anyone on the Fitzgerald try to contact the Crystal via bridge-to-bridge comms? Signal lights?
The Crystal is not a tanker.