A Thundercoil Harpoon in its pre-launch state. It is one of the primary armaments of the super-heavy Knight Valiant.

The Thundercoil Harpoon is one of the primary armaments of the Dominus-class Knight Valiant, which is a super-heavy Imperial Knight specialised for close combat. The Thundercoil Harpoon is a rather unusual weapon: it is a huge spear of adamantium fitted with pneumatic grapnels and attached by thick chains to an electrothaumic generator, allowing it to be fired then reeled back in time and again.

Not only does its impaling mass gouge massive wounds in larger targets while crushing smaller victims outright, but once the harpoon has hit home, the Noble pilot can trigger their generator and send a massive electrical charge through the chain. Arcing electrogheists leap from the harpoon, cooking monstrous beasts from the inside out and overloading the circuitry and power supplies of enemy war engines.