Flammenwerfer

Flame trooper is one of the Nazi bastards who don't need brown pants when you come into play. Instead, they tend to make commandos reconsider their choice of wardrobe. Capable of turning the battlefield into a fiery hell with a single sweep of their weapons, and clad head to toe in thickly padded heat-resistant armour, the specialist Flammenwerfer troopers can be utterly deadly, especially in tight quarters. They are not without their weaknesses, however. The weight of their weapon and all that protective gear makes them slow and clumsy, and the fuel tanks strapped to their backs are a notable weak spot in their defences. Their complete disregard for the safety of their fellow soldiers can also be turned to your advantage.

Tactics
The flame troopers don't announce their presence, short of the bellowing, deep voice that's usually drowned out by shrieking in various dialects of German. You will, however, see them early with their slow gait and measured advance towards you. They are a threat on open maps like Trainwreck and an absolute lethal danger in confined areas. They shoot fast and the flames they do are incredibly damaging, capable of eating through your health in seconds. Worse yet, they can take an abysmal amount of punishment.

Your best bet? Keep your distance or get in cover as soon as possible. The flames can't touch you if they can't reach you. Then roll a few grenades his way or get way back and go for headshots. The Recon Warcry works well for dealing direct damage, although the auto-aim interferes with the ability to drill high powered rounds into his face. If you're downed (and you will be), focus fire on him and go for headshots. It's perfectly possible to sacrifice yourself and wipe him out if you have enough ammo or upgrades.

Alternatively, go for the tank on his back and detonate it to put him out of his misery permanently.