Mercenary ships?

[Ludens]

In the Late Republic with all its turmoil we hear of many pirates and the Romans often tried to clear the sea of them (as they disrupted the vital grain supply). Quintus Sertorius was allied to a Cilician pirate lord, Caesar himself was captured by pirates, Pompey "cleared the seas" of them and I seem to Recall Augustus doing it again... During the principate being a pirate was probably somewhat more difficult as the Med was suddenly "Mare Nostrum". But as the Empire fell, piracy spread, just as it must have been prevalent before during the wars between the Diadochii.

Piracy was actually less prevalent before and during the wars of the Diadochii. It became a problem during the late Republic because, unlike the Diadochii empires and their predecessors, the Roman Republic did maintain a large standing navy. At this point there were no significant naval forces in the Mediterranean, making it a heaven for freebooters. The political turmoil of the late Republic didn't exactly help: the Senate was unwilling to allow a large concentration of force into the hands of one general or admiral, so anti-piracy actions were local and piecemeal. There were similar problems on the edges of the Empire: local rebellions and banditry were rife, but the Senate was more concerned with her own powergames. Both problems were solved with the introduction of the principate.

Back to the original topic: mercenary ships aren't unrealistic, as long as you cannot hire a serious navy this way. However, I wonder how the A.I. would deal with it. Would it understand that a naval invasion on a hired navy is a bad idea of the enemy has real warships?