In addition to the 20 mm MG 151/20 cannon, Bf-109 G6 was equipped with a pair of 13 mm MG 131 machine guns mounted in the cowling, firing over the top of the engine. Externally this resulted in two distinctive blisters over the gun breeches. The G6 became the most numerous version of the Bf-109: over 12,000 examples were built.