Flyers were anti-gravity warcraft used by the Roxolan Empire and other aliens to provide air support for their ground forces. In addition to carrying musketeers, the craft could also drop pots of gunpowder to terrorize primitive natives of targeted planets.
They were also used to take a luof down in an airlock and see if it survived. If it did, then the planet was safe for Roxolani.
Flyers proved to be vulnerable to human aircraft attack if approached from behind or below which were blind spots to their operators.