The Duchess is a rapid-fire Machine Gun able to be fitted to Main hardpoints.
The Duchess' moniker was originally pejorative in nature, stemming from its almost universal fouling issues and temperamentality. Eventually convinced it wasn't a case of user error, a small portion of the original development team returned to iterating on the weapon, at one point even embedding with a division of Duchess mounting Broadswords and Swedes. Prickly as they can be, the Design Bureau takes pride in its work, and after a dozen or so iterations across four years they had managed to turn the NEP's least reliable weapon into a thoroughly reliable mainstay.
Firing 40mm HEDP rounds at just over two per second, the Duchess combines a cannon's firepower with an MG's suppressive capability. Mounting a pair of the chain guns for asynchronous firing is a favorite tactic among Tinker drivers, and apparently some find the continuous vibration highly stimulating, though I cannot personally vouch for this.