“””””It is pretty much a universal military tradition that someone is always in charge, and that someone is the senior ranking individual present, regardless of rank. Which might be a Private First Class being in charge over a bunch of privates E-1 or E-2.
In protracted wars it is not that uncommon for an enlisted man (what the British call “other ranks”) to take command because all the officers have been killed or wounded but otherwise rendered combat ineffective. But someone is always in charge.””””””
You gave another good description, someone is “always in charge”.
The "between equals" needs clarification.
In the Air Force for example, line officers (command of operational, tactical, or combat units) and non-line officers (lawyers, chaplains, civil engineers, medical, logistics, finance) have distinct chains. A non-rated officer may outrank a rated officer but will not command line operations (aircraft, missiles, etc). A rated officer may outrank a non-rated officer but the rated officer will not direct the base operations (civil engineering, base security, the hospital, finance, etc).
Within each chain, in a pool of officers who were promoted on the exact same day, those with regular commissions would outrank those with reserve commissions. This has been a disappearing distinction since 2005 when all officers who entered active duty are commissioned as regular officers and all officers with reserve commissions were transferred to regular status, but there could still be a few individuals with reserve commissions due to age requirements. (We'd see this once in a while with someone who had an extended break in service - usually medical - who returned to Active Duty).
The Judge Advocate General (JAG) and Area Defense Counsel (ADC) usually fall under a district, not a base or a wing. Their chain of command would cross different bases and even Major Commands.
Medical officers are also normally outside the chain when deployed so as to maintain the separation required for international humanitarian law.