The BK 27 is a 27 mm (1.063 in) caliber revolver cannon manufactured by Mauser of Germany. It was developed in the late 1960s for the MRCA program that ultimately became the Panavia Tornado.

A revolver cannon is a type of autocannon, commonly used as an aircraft gun. It uses a cylinder with multiple chambers, similar to those of a revolver handgun, to speed up the loading-firing-ejection cycle. Some examples are also power-driven, to further speed the loading process. Unlike a rotary cannon, a revolver cannon only has a single barrel, so its spun weight is lower. Automatic revolver cannons have been produced by many different manufacturers.