Royal Fleet

The Royal Fleet is the naval force directly commanded by the King on the Iron Throne. It consists of a large number of ships based at King's Landing and Dragonstone. During the War of the Five Kings it became divided between the forces of King Joffrey Baratheon and Stannis Baratheon.

Season 2
When Stannis Baratheon declares himself king, he assumes command of the large portion of the Royal Fleet based at Dragonstone. This then becomes "his" Royal Fleet. Stannis then augments the Royal Fleet by recruiting an additional thirty warships belonging to Salladhor Saan.

Matthos Seaworth and his father debate the nomenclature of what to call "the Royal Fleet" where there are several kings in the realm. Later, when Stannis's forces approach King's Landing, King Joffrey Baratheon expects the twenty warships of the Royal Fleet squadron based at King's Landing to sail out to meet them. However, Tyrion Lannister, Acting Hand of the King, has ordered the Royal Fleet to fall back so as not to be destroyed by Stannis's numerically superior forces. Instead he commits a single ship packed with wildfire to the attack and has Bronn detonate the vessel when it has passed through the leading elements of Stannis's fleet. The resulting explosion destroys a large portion of Stannis's fleet and kills thousands of men. It is the opening move of the Battle of the Blackwater. Tyrion's move ensures that nineteen warships of the Royal Fleet survive the battle.

In the books
According to semi-canon material approved by George R.R. Martin, the Royal Fleet consists of 210 warships, at least 80 of which are full warships dipping 100 oars or more. The Royal Fleet's flagship is the King Robert's Hammer, which dips 400 oars and is the largest warship in Westeros. The Royal Fleet is divided into two squadrons, a smaller one of 50 based at King's Landing and a larger force of around 160 ships based at Dragonstone. The position of Dragonstone and the size of the fleet there makes an attack on King's Landing by sea almost impossible to mount for any foreign power.

In the Song of Ice and Fire novels, when the War of the Five Kings breaks out, Stannis Baratheon seizes control of the ships at Dragonstone and uses them in his attack on King's Landing. Unlike in the TV series, the Royal Fleet does participate in the Battle of the Blackwater in the books. The fleet engages Stannis's force and draws them into the mouth of the Blackwater Rush. Tyrion raises a massive chain to trap the fleet in the river and detonates barrels of wildfire hidden on the floor of the river and inside several of the royal ships. This move destroys most of Stannis's fleet, but also more than half of the Royal Fleet.

At the conclusion of the battle, only about a dozen ships of the Royal Fleet are still afloat. The rest have been obliterated by the wildfire (including the Queen Cersei) or severely damaged and forced into dock for repairs (such as the King Robert's Hammer). The destruction of the King's Landing dockyards, forcing the damaged ships to limp up the coast to Duskendale for repairs, makes the situation even more desperate.

The Royal Fleet is one of only several fleets operated by Westerosi forces. The ironborn maintain many hundreds of longships, including the formidable Iron Fleet (which consists of almost all of the ironborn's larger warships and galleys). House Redwyne also commands a substantial fleet based at the Arbor. After the Royal Fleet's near-destruction, the Redwyne Fleet becomes the largest fleet under the authority of the crown. House Lannister maintains a small coastal fleet at Lannisport (burned during the Greyjoy Rebellion but subsequently rebuilt). House Stark has had no strength at sea since Brandon the Burner destroyed the Northern fleet, after his father sailed west into the Sunset Sea and never returned.

Amongst foreign powers, Braavos is also reported to possess a formidable naval fleet, the strongest on the Narrow Sea. Its arsenal is said to be capable of assembling a war galley in less than a day. Volantis, Myr, Lys, Tyrosh, Elyria and Tolos are also said to possess respectably-sized fleets. However, the most famed and respected seamen in the world are from the Summer Islands.