A Battle-Barge is a large capital ship employed by Space Marine fleets. With the exception of the mobile fortress-monasteries employed by some Chapters, they are the largest capital ships available to the Space Marines. A Chapter will generally have two or three, though some have more (e.g. the Ultramarines have five and the Space Wolves have EIGHT).
The term itself is more of a ship type than a specific pattern; the Adeptus Mechanicus does produce a special pattern of ship just for Space Marines, but any ship can be used as a battle barge so long as it has enough capacity to launch vast quantities of Thunderhawks and Drop Pods and enough weapons and armor to protect them. A standard battle-barge has the facilities for three entire companies to operate out of, including support staff and logistics, such as vehicle repair.
No matter what they start as, or what they look like, battle-barges (like all Space Marine starships) are specialized for planetary assault. They have relatively little long-range firepower, but instead have enough hangar and torpedo bay capacity to launch three full companies of Space Marines at once, perform an orbital bombardment, or even commit Exterminatus.
Notable Battle Barges
Daughter of Tempests
A Lamenters Battle Barge deployed during the Corinth Crusade, in support of the Ultramarines.
While crusading the glorious motha-fukas of the most put upon Chapter in Imperial history learned of an Ork slave world cheerily named Slaughterhouse III. When the Lamenters were told that no other forces could be spared to free the world from the greenskin menace, they took it upon themselves to do so. When Daughter of Tempests jumped to the system, she intentionally emerged from the warp absurdly close to the Orkish defenses of the planet; the greenskins were taken by surprise and didn't get a shot off before the Daughter had disabled the orbital guns and deployed 300 yellow armored Sons of Sanguinious to the surface. She then assisted in the evacuation of 3 million survivors before the Lamenters declared Exterminatus to deny the Orks access to the planet's resources.
She was destroyed during the Badab War when theMinotaurs ambushed the Lamenters Chapter Fleet and forcibly boarded their ships.
When "Those Knife Eared Assholes" swiped the Salamander Strike Cruiser Forgehammer from Real Space and stashed it in their City, Vulkans Wrath lead a fleet Of Salamanders, Howling Griffons, and Silver Skulls into Commorragh itself to rescue their brothers. With the forces of 3 Chapters of Space Marines wreaking havoc in the streets, the missing cruiser was located, held down by an Electric Spire. Terminators deployed from Vulkan's Wrath teleported to Forgehammer's decks and loosed the cruisers missile battery on the spire. With Forgehammer free, Vulkan's Wrath lead the strike group out of the Dark City and into the safety of Imperial space.
The Flag Ship of the Astral Knights.
Tempestus was the battering ram on which the Astral Knights rode to their Glorious Destiny in the battles against the World Engine.
After the destruction of the World Engine and the entire chapter, Tempestus was salvaged and converted into an Imperial Shrine dedicated to the 772 Heroes of the Astral Knights on the world of Safehold, the last planet scoured by the World Engine.
Introduced in Battlefleet Gothic, the Seditio Opprimere is an Ultramarines ship that alarmed the Administratum and the Imperial Navy due to the modifications done to it in the wake of the First Tyrannic War. Y'see, the Seditio is a dedicated Lance boat, with many of its launch bays replaced instead by massive Lance batteries.
While the Ultramarines gave (a perfectly valid) excuse that the modifications were for clearing the space-lanes of Ultramar of any and all lingering Tyranid bio-ships in the wake of Hive Fleets Behemoth and Kraken, in practice this meant that the Smurfs now had a dedicated battleship killer, which the Space Marines (at that time of fluff) shouldn't have.
And kill battleships on the tabletop it did. It was so killy that it had to eventually be nerfed, with its Lance batteries replaced instead by much shorter-ranged Bombardment Cannons.
In Battlefleet Gothic
The Battle-barge is the biggest available to Space Marine fleets, comparable to an Imperial Navy Battleship. Due to the lack of Lance weaponry (ignoring the Seditio) however, the Battle-barge is more geared towards mid-to-short range brawls, and despite the forward-facing Torpedo tubes it gets by default, a player will mostly rely on its Weapons Batteries, Launch Bays, and Bombardment Cannon to do its work.
Due to its armor and shields, plus the Space Marine crew, its more than capable of getting in close and dealing pain.
In Battlefleet Gothic: Armada (1 & 2)
The Battle-barge is one of the toughest ships available, with excellent armor and shields. Due to its Space Marine crew, the ship is immune to Morale Loss, and much more effective at boarding actions.
The ship comes in two flavors in-game, with one featuring the "classic" close-range brawler weapons configuration of Torpedoes (standard or Boarding), Macrocannons and Weapons batteries, while the other gets the Seditio suite of long-ranged Lances on top of the Torps. Both versions retain their Launch Bays for fighter or bomber support.
Regardless of your choice, it's best to keep in mind the point costs, as these ships are also much more expensive than their counterpart in the Imperial Navy.