In "Black Tuesday", Derek "Frost" Westbrook plants some Thermite on the base of an enemy communications relay, lighting it with a wireless clacker (similar to the one used to detonate C4) and in the process destroying it.
It also appears in the Special Ops mission Over Reactor where the player has to disarm it before they can enter the submarine.
Thermite in Call of Duty: Modern Warfare 3.
The Thermite on the Jamming Tower in "Black Tuesday".
Approaching the Thermite on the submarine in "Over Reactor".
The Thermite makes it debut in Call of Duty: Black Ops III as a lethal equipment unlocked at level 29, where it ignites to cause a radius of fire to burn on the ground. It works similarly to Nova Gas Grenades from Black Ops, except that Thermite is much more damaging to players, lasts a shorter duration, and covers only a circular area on the ground instead of the spherical area the Nova Gas covers. Thermite is easily distinguishable from the blue flames emitted on the ground, and as such, can be deemed useless if used aggressively, as enemies that see it from afar can alert their teammates about the hazard. However it can be used effectively to flush enemies out of certain areas allowing your team to push forward or take out a group of enemies who have an area locked down.