Short answers, pulled from the story.
The traditional founding date of the Roman navy is around 311 BC, when two officials called the duumviri navales were appointed to maintain a fleet. That first fleet consisted of 20 ships, most likely triremes, with each official commanding a squadron of ten.
The corvus was a long plank fitted with a metal spike that could be dropped onto an enemy ship to lock it in place. Roman marines then used it as a boarding bridge, turning sea combat into hand-to-hand fighting where Roman legionaries had the advantage. It was deployed effectively at the Battle of Mylae in 260 BC under Gaius Duilius but was later abandoned because its weight made quinqueremes unstable in rough seas.
In 67 BC, the Lex Gabinia granted Pompey unprecedented authority and resources to act against the pirates. He launched a coordinated campaign and cleared the pirates from the Mediterranean in only three months.
The two praetorian fleets were the Classis Misenensis and the Classis Ravennas, both established in 27 BC and based in Italy. They served as a central naval reserve directly available to the emperor, with duties spanning patrol and transport missions across the entire Mediterranean.
No. Throughout the Roman navy's history, rowers called remiges were men of free status. Slaves were employed only in extreme emergencies, and even then they were freed before serving. In the imperial period, the bulk of crews came from non-citizen freeborn provincials, particularly Greeks, Phoenicians, Syrians, and Egyptians.
The Western Roman navy declined through a combination of third-century neglect, barbarian seizures of ships, and catastrophic losses. By the mid-fifth century, the historians Priscus and Sidonius Apollinaris both confirm the Western Empire essentially had no war navy. Fleets mobilized against the Vandal Kingdom in 460 and 468, under emperors Majorian and Anthemius, ended in disaster, leaving the Vandals free to raid the western Mediterranean unopposed from their base at Carthage.