During GDI's assault on Kane's temple in Cairo, several Mammoth tanks were found near a TW1-era GDI base, still in operating conditions despite decades of neglect.
Mammoth tanks cannot be built, and only appear during certain campaign missions. Most notably, three Mammoth tanks can be found in Final Conflict, at an abandoned GDI base near the northwestern Nod base. Once approached, they can be controlled by the player.
In the Nod missions Sheep's Clothing (TS) and Mutant Extermination (FS), they appear as enemy units, being the heaviest vehicles used by the Forgotten. They are individually powerful, each capable of taking on two Tick tanks. However, they are few in number, and the Forgotten cannot construct more.
The Mammoth tank is armed with a pair of powerful cannons and anti-air missiles. It is also extremely durable and also has the ability to self-repair to 50% health (though it cannot do so if its health is less than 4%). Its greatest weakness is its very slow speed, which can leave it vulnerable to enemy artillery and stationary defenses.
A mid-development Tiberian Sun screenshot showing Nod-controlled Mammoth tanks