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An ancient pict-capture of a Sons of Horus Legion Mastodon during the Horus Heresy

The Mastodon Heavy Assault Transport, or simply Mastodon, is a super-heavy assault transport that was utilised by the Legiones Astartes during the Great Crusade and Horus Heresy. The Mastodon was one of the heaviest assault transports ever used by the Space Marine Legions, and was reserved for use against only the most heavily fortified of enemy positions. At several times the size of a Land Raider, the Mastodon was a truly formidable warmachine, capable of ferrying up to forty Space Marines, or twenty Marines and two Dreadnoughts through the most perilous of battlefields and protecting them from the most powerful of enemy weapons, including Titans. Although Mastodons were used by nearly every Legion, they were used sparing during the later Great Crusade as deploying them was a major operation in itself, being mostly deployed during long protracted siege operations where one or more entire Legions had amassed to destroy a foe that no other was capable of engaging. As the Horus Heresy ground ever onward the Mastodon saw an increase in its deployment rate, as both sides of the conflict committed every last weapon and vehicle to utterly destroy their hated foe.

Combat RoleEdit


A Mastodon of the Sons of Horus crossing the battlefield

The primary combat role of the Mastodon was the safe delivery of its Astartes passengers directly into the enemy defences, and usually used to breach fortified walls or structures using its forwards firing Siege Melta Array and heavy armoured prow. The Mastodon's forwards Siege Melta Array could create a breach through even the thickest of enemy walls, few fortifications could withstand this fearsome weapon. Once the Mastodon creates a breach powerful interior servos fire the assault doors open, smashing aside debris and unfortunate enemies and allowing the Space Marines within to press directly into the heart of the enemy's position. Once the Space Marines begin to cross through the breach the rear ramp lowers, allowing more squads to funnel through the Mastodon and into the enemy stronghold all the while being protected by the Mastodon's heavy armour and weaponry as the Mastodon itself acts as an armoured breach tunnel.



A cutaway of the interior of a Mastodon showing the armoured tunnel and bulkheads

The Mastodon is designed as the ultimate siege transport, carrying a large group of infantry straight up to the enemy's walls, breaching said walls, and protecting the infantry as they pour through the vehicle and into the interior of the enemy fortress or stronghold. The interior and exterior of the Mastodon is heavily armoured, with an armoured shell acting the interior tunnel portion of the vehicle and armoured ceramite plating protecting the exterior from enemy fire. The inside is subdivided into different sections with armoured bulkheads that protect the different areas from fire and damage, opening to allow infantry to progress through. The vehicle's upper deck is where the driver and crew are stationed, with hatches and portholes allowing officers to direct the battle around them. The entire vehicle can be sealed closed in case the enemy makes use of chemical or viral weaponry. The reinforced interior shell and thick exterior armour can protect the vehicle so well that even when suffering from catastrophic damage the vehicle may simply be reduced to a nearly indestructible wreck of twisted metal, acting as a small bunker that can protect those who need shelter from the storm of battle outside.


The Mastodon was as heavily armed as it was armoured, with a wide variety of weapons and technology it was fully capable of defending itself and its cargo from attack. The most important weapon of the Mastodon was its fixed forwards-firing Siege Melta Array, an array of nine melta-weapons that was used to burn through enemy walls and fortifications. The secondary weapons of the Mastodon include a turret-mounted Skyreaper Battery for protection from enemy flyers, two sponson-mounted Heavy Flamers , and two sponson-mounted Lascannons . The Mastodon commonly comes outfitted with Smoke Launchers , a Searchlight , and Armoured Ceramite Plating and can also be equipped with up to four Hunter-Killer Missile Launchers . The Mastadon can be used a command tank, and its Skyreaper Battery can be completely replaced with a command vox relay system. The Mastodon is also equipped with two Void Shield Generators, providing even more protection from enemy fire.

Known CampaignsEdit

The following is a list of known campaigns that Mastodons were used in:

  • Kharaatan Campaign - The Salamanders Legion used nearly 150 Mastodons during the Kharaatan Campaign to transport the entirety of their forces on the ground, approximately 6000 Space Marines.
  • Signus Campaign - At least one Mastodon was used by the Blood Angels Legion during the Signus Campaign, this single Mastodon was used to carry Blood Angels across the battlefield to the Chaos Temple known as the Cathedral of the Mark. This Mastodon was torn apart and eventually abandoned when it became trapped in massive thorns near the temple.
  • Thramas Crusade - The Iron Hands Legion used at least eight Mastodon's against the Death Guard Legion. Death Guard Grave Wardens eventually captured the eight known Mastodons.
  • Xana Incursion - Loyalist World Eaters under the command of Endryd Haar repainted at least one Mastodon in the livery of the Sons of Horus to deceive the Dark Mechanicum Magi of Xana.

Notable MastodonsEdit

The following is a list of notable Mastodons:


The Ios Est, a World Eaters Mastodon cunningly repainted in the livery of the Sons of Horus

  • Ios Est - The Ios Est was a near enigmatic Mastodon believed to have come from the World Eaters Legion, possibly belonging to World Eaters Loyalists under the command of Endryd Haar. During the Xana Incursion a Mastodon codified as the Iso Est bore the livery of the Sons of Horus Legion and was used to deceive and attack the Dark Mechanicum at Xana. The vehicle was believed to have been destroyed on Xana V as being unmasked when the World Eaters launched their suprise attack against the isolated Forge World. The Ios Ests ultimate fate is unknown, although unconfirmed reports describe a Mastodon, its armour scoured to bare metal, in service with the irregular forces commanded by Endryd Haar during the battles for Beta-Garmon and even during the Siege of Terra. This is however unlikely, but many things from the Age of Darkness are unknown, lost in mystery.

Adeptus Mechanicus Technical SpecificationsEdit

Mastodon Heavy Assault Transport
Vehicle Name: Mastodon Main Armament: 1 Fixed-forwards Melta Siege Array , 1 Turret-mounted Skyreaper Battery
Forge World of Origin: Unknown (Presumably many during Great Crusade) Secondary Armament: 2 Sponson-mounted Heavy Flamers , 2 Sponson-mounted Lascannons
Known Patterns: Unknown Traverse: Unknown
Crew: Unknown Elevation: Unknown
Powerplant: Unknown Main Ammunition: Unknown
Weight: Unknown Secondary Ammunition: Unknown, and Unlimited (Powered from Engines)
Length: Unknown Armour:
Width: Unknown
Height: Unknown Superstructure: Unknown
Ground Clearance: Unknown Hull: Unknown
Max Speed On-Road: Unknown Gun Mantlet: Unknown
Max Speed Off-Road: Unknown Vehicle Designation: Unknown
Transport Capacity: 40 Space Marines or 20 Space Marines and 2 Dreadnought s Firing Ports: N/A
Access Points: One Rear, One Front Turret: Unknown


  • The Primarchs (Anthology Novel), "The Lion" by Gav Thorpe, pp. 291-293
  • Fear To Tread (Novel) by James Swallow, pp. 105, 419-420, 425-426, 428, 431
  • Angel Exterminatus (Novel) by Graham McNeill, pp. 221-222
  • Vulkan Lives (Novel) by Nick Kyme, pp. 36, 41, 45
  • White Dwarf 106 (February 6th, 2016) (Digital Edition)


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