The Romans are not remembered as a maritime superpower. In fact, they didn't have much of a navy to speak of until the First Punic War (264 BCE). It was these wars against Carthage which acted as a catalyst for Rome to develop a naval force to control the entire Mediterranean basin.
Beginnings of the Roman Navy
Up until 264 BCE, it was Carthage who dominated the western Meditteranean waters. For Rome to defeat Carthage, it had to build a fleet from scratch, and train sailors and soldiers fight on the seas. This was a monumental challenge considering Carthage's massive headstart in naval warfare.
To level the playing field, Rome invented the 'corvus', which is essentially a drawbridge. The Roman ship would ram into the enemy and then the corvus would be lowered, allowing the Roman soldiers to rush onto the enemy ship. This introduced infantry, hand-to-hand, combat into naval battles, something Rome happened to excel in.
After Rome had conquered the entire Mediterranean basin, it could be used for transporting soldiers and trade with little risk. The only danger on the seas came from pirates, who were a source of constant irritation, and it wasn't until 67 BCE when the Senate passed a law (Lex Gabinia) granting Pompey the Great extraordinary powers to neutralize the pirate threat.
Those who joined the Roman navy were not given the same prestige as those who had joined the legions. Often the navy consisted of men who could join the army for whatever reason. Sailors would serve for twenty-six years, after which they would receive full Roman citizenship.
The Roman warship of choice was the trireme. It was thirty-five meters long and around five meters wide. They were developed to be as lightweight as possible to provide maximum maneuverability in battle. The Romans also used a variety of other vessels, some very heavy warships, and other lighter and quick ships. Here's a list starting with heavier warships to lighter more nimble scouting ships:
Some of these larger vessels utilized around three-hundred rowers each. It would be the responsibility of the oarsmen during a battle to maneuver the ship around the battlefield. This meant that the outcome of a conflict often came down to the ability and fitness of a ship's rowers.
Weapons and Tactics
Naval battles were fought quite close to the coast. This allowed admirals to dispose of as much weight as possible before battles. The lighter the ship was, the more maneuverable it was. This included removing the ship's mast and rigging before each battle and leaving it on the shore.
The objective all naval tactics was to divide and separate the enemy fleet and destroy isolated vessels. Various factors affected the outcome of a naval conflict:
Ships had a variety of weapons:
Ships would have to regularly undergo maintenance in dry docks to allow the ship's wood to dry out. If left at sea for too long the wood would become saturated and slow the vessel down. Additionally, fleets would often have to re-stock at ports as space on board was limited.
Through the Ages
At the start of the Roman Republic (509 BCE), Rome did not have a navy. Its territories did not expand much beyond the city itself. It was not until 311 BCE that the fist Roman naval fleet was built. Twenty ships were constructed to assist in the conquest of Campania, to the south of Rome.
It was not until the start of the First Punic War (264 BCE) that Rome began to assemble a fleet capable of fighting against other civilizations. It was the investment in this fleet which allowed Rome to crush Carthage, razing the city to the ground 146 BCE.
Rome's fleet was then put to use in the Adriatic Sea and dealing with Illyrian pirates. The Roman navy was next utilized in the Macedonian and Seleucid Wars. While most of these wars were handled on land, the naval forces were used to wrest control of the eastern Mediterranean. Following these two conflicts, Rome's naval capabilities overwhelmed any other in the region.
The next naval conflict of note was not a foreign threat but the civil war which would bring an end to the Roman Republic. The Battle of Actium (31 BCE) between Octavian and Mark Antony. Octavian was victorious, and Rome's navy declined in importance as land based conquests in Europe and beyond took precedence.
During the early Roman Empire, there was little naval activity, with it predominantly being used to transport soldiers and protect trade routes from pirates. However, it did play a significant role in numerous campaigns, for example, Trajan's conquests in Dacia. This was a common theme throughout the Roman Empire; the navy played a supporting role in many of Rome's land-based conflicts.
In the 5th century CE, the Vandals invaded northern Africa and were able to capture a Roman fleet. Using this fleet they were able to terrorize Roman owned lands. Rome failed to respond to this invasion with power and was forced into a non-favorable diplomatic resolution.