"Navigare necesse est; vivere non est necesse..." -- Gnaeus Pompeius
Despite turning the Mediterranean into "their sea," neither the Roman Republic nor Empire put a high priority on naval power, except for brief crises periods requiring the hurried building of a fleet. The army was the senior service; the navy was the junior, and thus open to non-Romans as a career. Except for the head-on wars with the dominant naval power of the day (Carthage), the Roman navy relied for day-to-day service on the trireme (three banks of oars), the fast, light liburnian galley, and even a few quads (quadriremes, which had four rowers to each oar). Quinqueremes had five rowers to each oar, and were used during the big fleet confrontations with Carthage. Quinqueremes - though less maneuverable -- had the advantage that, with five rowers to each oar, less individual skill was needed than aboard a trireme or liburnian, where there was one rower per oar. The liburnian was a borrowed design which had originated along the Dalmatian coast (roughly modern Croatia). Half the beam of a trireme, it had almost the same number of oars, and was considerably faster. Liburnians became the shipkillers in the battle line. If you were an important government official and needed to get somewhere fast, the liburnian was your ship. The Roman navy possessed a few Sixes and Sevens (so named from the number of rowers on each oar), but these were even larger and less wieldy ships.
The historian Polybius describes Roman quinqueremes being built in 60 days from cutting down of the first tree to launch. (Green wood? They must have leaked like sieves!). To maximize training time, crews learned to row on wooden stages erected on land while the ships were under construction. (Perhaps we should retranslate "Cogito, ergo sum" to "I think; I erg; I am!") Crews were sometimes conscripted or borrowed from allies, but they were not slaves chained to their oars. (A misconception arising from a mis-translation of the word for sailors who received Roman citizenship upon completion of their service). The pay and opportunity for citizenship made naval careers attractive, and volunteers were usually plentiful. Rome relied heavily on non-Roman sailors (esp. from Greece, Egypt, and Dalmatia) to crew its ships, placing a handful of its own officers (often army, and sometimes not speaking their crews' languages) over them. (Heavily-recruited Balkan rowers...? Some things never change.) Roman fleet structure, nautical terms, and practice were borrowed wholesale from the Greek navies.*
The Romans fought their sea battles with land tactics - boarding and fighting hand-to-hand on the decks. Landlubbers commanding fleets frequently led to disasters, especially those who lacked a healthy respect for the changeablity and force of weather. Maneuvering fleets of oared vessels requires skill and experience. The ships were vulnerable to being knocked beam-on to large waves (their high bows made them difficult to hold into the wind). Once parallel to the waves, they were unmaneuverable and prone to swamp or capsize. Three times in seven years the Romans lost more than 100 warships at a time to single storms when commanders ignored the advice of the professional sailors. During the second Punic War -- within weeks of the Romans winning what ought to have been the decisive victory of the war -- they smashed all but seventy ships of their entire navy -- plus captured ships -- onto the coast of Sicily (don'tcha hate it when that happens?), setting them back even with their adversaries.
Several spectacular mutinies occurred, notably in AD 70 after the Romans violated the terms of a longstanding treaty with their Batavian (Dutch) allies, and the Batavian crews of the Rhine fleet rowed their ships over to the rebels while their Roman officers were either executed or swore futilely at them. In AD 84, some soldiers of the Usipii (a German tribe) stationed in Britain, stole three ships (one escaped and returned to base) and went for a summer joyride raiding northern Britain and Denmark until the pilots escaped and the mutineers wrecked the remaining two ships in the Frisian Islands.
On 25 August of AD 79, Pliny the Elder -- the praefect (admiral) of the fleet at Misenum -- was overcome by fumes during the eruption of Versuvius while his quadriremes - hampered by onshore winds and pelted by falling pumice -- were attempting the hazardous evacuation of Pompei's residents. According to his nephew, Pliny sailed into the danger commenting to his helmsman, "Fortes fortuna iuvat" (Fortune helps the brave.)
After Roman land conquests turned the Med into a Roman lake, the navy's chief duties were anti-pirate patrols, ferrying dispatches and government officials, and operating in close support of the land forces (e.g. the powerful Rhine fleet). Upon the collapse of the Empire, the Visigoths (whom the Romans had employed as crews in larger and larger numbers because of their nautical skill) acquired the remaining assets of the Roman navy. Same ships/personnel; new management/new unis. The main Roman naval base at Ravenna is now a park, having silted up since that time.
"Parate omnes; remigate!"
* see Cybernetics - Rowing in the Athenian Navy, Believers column, 27 November, 2000