The flame tank, nicknamed "Devil's Tongue" (also known as the "Pyradon" flame tank), was an experimental multi-purpose weapon developed by the Brotherhood of Nod by the time of the First Tiberium War. While they were decommissioned by Nod forces by the Second Tiberium War in favour of the Devil's Tongue subterranean flame tank, some of these vehicles were commandeered by the Forgotten by the time of the Firestorm Crisis.
By its stats, it is equivalent to its subterranean successor.
The Devil's Tongue carries twin fixed flame cannons joined to two large pressurized napalm tanks on its back. The driver's canopy is located between the giant flamethrowers. The whole vehicle rests on a light tracked chassis.
The resulting tank is a fast, versatile and nightmarish weapon, dangerous to infantry and buildings alike, as shown in the test footage recorded during the first Tiberium War and archived news articles below - but also lightly armoured and highly volatile, taking everything with it or horribly burn in the blast radius when destroyed, including friendlies. Results are hot indeed.
The flame tank's model is actually contained in the vanilla Tiberian Sun files, along with several other unused voxels based upon units from Tiberian Dawn, which were likely used as placeholders. It was not until Firestorm that the unit was coded.