Military priests in Late Empire armies?

[Robert Vermaat]

Secondly, no priest could - technically - operate outside the authority of a bishop and be considered orthodox. I know of no 'military bishops' in Late Roman times, though today IIRC that is how many Western nations run their armed services chaplaincies.

Bishops were for a large part powerful men turning to the church.
Some of them were wealthy civilians, some retiring civil servants, some military men.
For instance, we have St. martin of Tours who supposedly was a commander. Or St. Germanus of Auxerre who is said to have held a rank in the defence of Armorica, and who lent some assistance against Saxon raiders in Britain as a bishop.
When Arbogast, the Frank who held Belgica I, delivered his province to Clovis in 486, he may well have been ordained bishop of Carnotense (Chartres) or taken the office voluntaruily - it was not without influence.
The Emperor Avitus was deposed in 456 and forced to become a bishop on the spot (though some say he was strangled or starved).
The usurper Glycerius abdicated in 474 and became bishop of Salonae (Salona).