Imperial Roman military titles?

[Renatus]

If your book is in the future and everything is *space* themed: why assume naval titles?

On the other hand, if it involves spaceships I assume that nautical terminology could be appropriate.

. . . smaller provinces were governed by procurators from the equestrian order.

And to add even further confusion, in the Julio-Claudian period such provinces were governed by prefects. Pontius Pilate was a praefectus.

[Nathan Ross]

in the Julio-Claudian period such provinces were governed by prefects. Pontius Pilate was a praefectus.

Judea really demonstrates how complex this could become! - initially it was governed by a praefectus as a sort of annexe of Syria, then under Claudius the praefectus was upgraded to a procurator. After the Jewish Revolt in AD70 there was a legion stationed there, so a senator took over as legatus propraetor, then under Hadrian another legion was added to the garrison and the governorship was promoted to proconsular rank. Then, after the Bar Kokhba revolt, the whole province was merged with part of Syria and renamed Syria Palaestina, governed by a proconsul. Later still the province was split into Syria Palaestina and Syria Coele, each under a legatus propraetor, and both of these were later replaced by equestrian praesides...

[Frank]

Judea really demonstrates how complex this could become!

Just to confuse even more: During a revolt in Mauretania a legion was moved to this province, which was governed by a procurator. During this campaign the equestrian commander acted as praefectus pro legato.

That was long before the 3rd century, when praefecti vice legati and later simply praefecti legionis became the rule.

The problem is, that praefectus, procurator, tribunus or legatus are not military ranks. Because these are terms from different careers depending on the social ranking (eques, senator, ...)
These terms are rather functions than ranks.

If there was something like a ranking system at all, it is the system the romans introduced during the 3rd century: vir egregius, vir clarissmus, vir perfectissimus, ....