Rüstsatz Rüstsätze were field modification kits produced for the German Luftwaffe during the Second World War . They were packaged in kit form , usually direct from the aircraft manufacturer , and allowed for field modifications of various German aircraft used in World War II , predominantly fighter bombers and night fighters . Rüstsätze kits could be fitted in the field , as opposed to Umrüst - Bausätze kits , which were typically fitted in the factory . This was not a hard and fast rule , however ; during production runs various Rüstsätze kits were often fitted by factories in order to meet Luftwaffe demands , and " / R " designations were also occasionally applied to more complex changes in an aircraft ' s airframe design that were much more suitably completed at production line facilities , as with a few of the " / R " - designated versions of the He 177 A - 5 heavy bomber . Typical Rüstsätze kits would include extra cannon or machine gun armament , most often mounted in underwing gun pod s , bomb and drop tank fittings , extra armor , fuel , and various electrical system upgrades . The kits were numbered R1 , R2 , R3 and so forth . Some of these upgrades would become almost standard on certain fighters . The nomenclature was often confusing , as each Luftwaffe aircraft type used their own unique series of / R - series ( as well as the factory fitted / U - series ) numbers : the " / R2 " kit for a Messerschmitt Bf 109 G was for the fitment of a pair of the powerful Werfer - Granate 21 ( WGr 21 ) underwing mounted rockets , while the Focke - Wulf 190 used the " / R6 " designation for this same exact fitment . The Focke - Wulf Fw 190 was well known for its various Rüstsätze , which included : R1 : Standard radio equipment upgraded to the FuG 16ZE ( as fitted to the FW 190A - 4 and A - 5 ) R1 : Addition of a WB ( Waffen - Behälter ) 151 / 20 cannon pod under each wing ( as fitted to the FW 190A - 6 , A - 7 or A - 8 ) R2 : Addition of an MK 108 cannon pod mount under each wing ( as fitted to the FW 190A - 6 and A - 8 ) R2 : Outboard wing mounted MK 108 cannon ( as fitted to the FW 190A - 7 , A - 8 and A - 9 ) R2 : Addition of wing mounted MK 108 cannons and a fuselage center line mounted WGr ( Werfer - Granate ) 21 rocket ( as fitted to the FW 190A - 8 ) R3 : Addition of wing mounted MK 103 cannon s ( as fitted to the FW 190A - 6 and A - 8 ) R4 : Addition of fuselage fitted GM - 1 nitrous boost system ( as fitted to the FW 190A - 6 and A - 8 ) R5 : Addition of fuselage fitted 115 liter fuel tank ( as fitted to the FW 190A - 8 ) R6 : Addition of two wing mounted " Werfer - Granate 21 " ( Wfr . Gr . 21 ) rocket launchers ( as fitted to the FW 190A - 4 , A - 5 , A - 6 , A - 7 and A - 8 ) R7 : Addition of armor to the cockpit ( as fitted to the FW 190A - 6 , A - 7 and A - 8 ) R8 : Addition of wing mounted MK 108 cannons and cockpit armour ( as fitted to the FW 190A - 8 and A - 9 ) R11 : Addition of FuG 125 radio , PKS 12 radio direction finder , and window heaters ( as fitted to the FW 190A - 8 and A - 9 ) and D - series airframes ( also used for the Ta 152 ) . R12 : Addition of FuG 125 radio , PKS 12 radio direction finder , window heaters and wing mounted MK 108 cannons ( as fitted to the FW 190A - 8 )