I've waited 30 years for this... The following article is about content that is not yet released. As a result, its content is subject to change.
The First Order's Heavy Assault Stormtroopers are an elite breed of Stormtrooper which specialize in wielding heavy blasters. They are their faction's Heavy class. Interestingly, they appear to carry F-11D Blaster Rifles like their Assault counterpart, and the weapon they're better known for using, the FWMB-10K Heavy Blaster, is instead unlockable (or available free for those who purchased the deluxe edition).
