I can understand that, if there is somebody who can move into a temporary senior command position. But what in the case of where everybody left is a private?
In the British military, when there is more than one person who is equally ranked, then they go by birthdate.
I’m just wondering about the American military, what steps do they go through to determine who is the senior officer if everybody is at the same rank?
Probably date of rank. Lots of “field promotions” in WW2 when no officers left someone is given an on the spot promotion to commissioned status. Often it boils down to every man for himself if it gets bad enough.h