The Gustav, the nick name of Bf-109 G6 was the most heavily produced variant of the 109 series. Wartime development tried to make the plane a more suitable bomber interceptor. Depending on availability of this bigger weapon, some Bf 109Gs had a nose-mounted 30 mm Mk 108 cannon instead of the 20 mm type. Also, some planes were fitted with Rustsatze (add-ons), like the R-6 modification kit adding two more MG151/20 20mm guns in under wing gondolas, for a better efficiency against allied bombers. As the War wore on efforts were made to upgrade the 109's firepower. Several compromises were made to make the Gustav a better bomber interceptor. 20MM cannon pods mounted gondola fashion under the wings are seen on the R6 Variant on War birds.