Darth Vader rarely(?) calls his subordinates by just name; even when he personally dislike specific imperial officers (like Ozzel) he usually adresses them in proper way, by their military rank. In Lost Command, the only one time Vader dropped that habbit and called Voca by only his name was the scene when the commander was visible upset by death of some of his troopers.
Maybe it’s just me, but that scene is quite powerful, you know? The clone commander who until now followed Vader’s orders - including the atrocious ones - without any protest, now doesn’t even try to hide his pain / sadness; his whole body language screams he is not emotionally well and Vader... doesn’t rebuke him in any way. The Lord of the Sith drops military rank and by addressing Voca like that made me feel like Vader... sounds more informal. In that scene he doesn't command the clone trooper, doesn’t demand a raport. I think Vader understands perfectly commander’s feeling about lost troopers and doesn’t treat it as a weakness. He asks how many of your squad have survived - not how many mine troopers - and this is what brings Voca back into “soldier mode” from such rare moment of visible emotional distress in clone trooper.
I don’t know even how to describe my feeling about this scene, but that moment really catched my attention. Because Vader so rarely drops the proper (”military”) way to address the subordinates. And that makes the whole Vader’s presence here more... gentle? human?