"From 'A Tolkienist's Perspective Blog' : a two part article part 1 part 2 about the military structure in Mordor.
There is a hierarchy chart if you want a summary.
Was the rapid collapse of the military following the destruction of the ring indicative of the fragility of this structure , and its susceptibility to a decapitation strike ? Would a flatter hierarchy or something similar to the Imperial Military or Starfleet have been more resilient?"
Right... I had meant to put an exception in regarding Minas Morgul, and any "troops" based there..
Somewhere in the mass of additional materials that have been published over the years I'm pretty confident I recall a statement that Khamul was in charge of Dol Guldur for many years, much in the same way that the Lord of the Nazgul was in charge of Minas Morgul.
Definitely. Given that Sauron founded Mordor in the Second Age and ruled it for about 2500 years before his realm was overthrown by the Last Alliance, then refounded it in the Third Age about 2000 years later and ruled for another millennia, talking about 'The' military structure of Mordor is like talking about 'the' military structure of the Roman Empire x 4 or 5. Still fun to think about though.
For example, in the 3rd Age, would Sauron have just attempted to rebuild his now-ancient force structures and tables of organization, or would he have modified them to reflect new realities, or just started from scratch? Did he even care about such things, or would he have just delegated such matters to the Nazgul and other lieutenants, worshippers, and lackeys? (In my headcanon he would have taken a keen interest, but YMMV.)