The Wechselapparat M1917, also known as the Wex, was a lightweight flamethrower developed from the Kleinflammenwerfer M.16 ("Kleif"). It was, along with several other flamethrowers of the era, developed by Richard Fiedler, as early as 1901. Fiedler's designs were formative to flamethrower technology and analogous designs remained in use for many years.
An exchange apparatus (wechselapparat) was fitted between its central compressed air tank and the outer ring fuel tank, a weight-saving improvement over the heavier Kleif that operated from a single tank. It also uses the same ignition system as the Kleif (a magnesium ignitor system).
The weapon appears throughout the campaign in the hands of Flame Troopers, making its first appearance in the opening mission Storm of Steel. Unlike in multiplayer, when shooting the tank on a flame troopers back, it will shoot out a small jet of flame for a few seconds until it explodes in a massive fireball that will kill anything around it within approximately 5 meters.
The weapon is the primary armament of the Flame Trooper Elite Class. When first firing, the Wex emits a stream of unlit fuel, which then ignites after a short delay. This means that enemies cannot be damaged as soon as the weapon is fired. It can cast flames a fair distance ahead, some of which may linger on the ground and walls. Although it carries unlimited fuel, it can only be fired for about 15 seconds at a time before needing a cooldown.
Damage is comparable to the Incendiary Grenade, with some damage inflicted after exposure.