How to unlock thermite in Warzone

Call of Duty: Warzone Season 3 adds thermite, a (kind of) new lethal equipment. If you're a lapsed Warzone player, that might sound very confusing, since it's been in the battle royale before, but this lethal was removed in the Black Ops 6 era, only to make a return this season in a baffling way.

Much like the new Monolithic Suppressor attachment, the in-game description telling you how to unlock thermite is broken. I tell a lie: there actually isn't even a description for this item at all...