A Battle Barge is the Astartes (Space Marines) primary warship. It’s heavily armored and prepared to carry and deploy large amounts of Astartes and war equipment. Its primary role is as command and low orbit assault and deployment vessel, but it’s also well prepared for space combat if the need arises.
The term Battle Barge isn’t associated with any specific ship class, but more with the role and function of the ship. Many of them are merely retrofitted battleships to serve under the Astartes fleets.
Battle Barges have been used since the pre-heresy era by the time Legiones Astartes. In the 40k millennium, they’re used by the Adeptus Astartes.
The primary function of a Battle Barge is to efficiently deploy large numbers of Astartes to a battle area. They are capable of deploying up to three companies of Astartes (about 300) simultaneously.
The deployment process is via dozens of Drop Pods. But they usually also carry three squadrons of Thunderhawks which can be used both as attack craft of orbit to land transports.
They possess strong defensive capabilities so they are able to penetrate hostile areas and deploy their deadly cargo.
The Battle Barge skeleton is made of an ultra-dense alloy that can only be mined from sites of recent volcanic eruptions.
This structure is then wrapped by hardened plasteel and adamantium.
The void shields are energy barriers are capable of can defend against weapon and explosive impacts
and are also capable of absorbing and deflecting stellar radiation and meteor showers.
Since they travel through the warp, battle barges are also protected by Gellar Fields.
These devices create a bubble of realspace around a ship as it passes through the warp.
Bombardment cannons are massive destruction weapons used to devastate ground defenses, to enable and protect boarding actions, and to aid deployed ground troops.
As a last resort, their raw power can also be used in ship to ship combat, but since they are close-range weapons this usage is very circumstantial.
Battle barges aren't suited for space combat but if the need arises their primary and deadly strategy is to use their drop pods to board the enemy ship and cause total destruction from the inside.
Ship to Ship
To enable the boarding of other vessels they possess ship-to-ship weapons that can be used to disable shields, such as Macro-cannons, Plasma projectors, Fusion Beamers, and Missile launchers.
Battle Barges are frequently called to execute Exterminatus.
For this end, they carry the world ending Cyclonic Torpedos and Virus Bombs.
A Battle Barge is usually from 6 to 7 km (about 4 miles) long. It carries 3 companies of Astartes, 3 Thunderhawk squadrons, and dozens of Drop Pods.