Junkers Ju 87 of 500 sorties per day and caused heavy losses among Soviet forces, losing an average of only one Stuka per day. The Battle of Stalingrad marked the high point in the fortunes of the Junkers Ju 87 Stuka. As the strength of the Soviet Air Forces grew, they gradually wrested control of the skies from the Luftwaffe. From this point onward, Stuka losses increased. The Stuka was also heavily involved in Operation Citadel, the Battle of Kursk. The Luftwaffe committed I, II, III./St.G 1 and III./StG 3 under the command of Luftflotte 6. I., II, III. of StGs 2 and
Junkers marked on the J-9's landing gear wheel covers. The corrugated duralumin wing and fuselage "skin" introduced in the J-series became a trademark of Junkers aircraft built in the 1920s and '30s. Development continued during the course of World War I, including a growing (but troublesome) partnership with Fokker, as the "Junkers-Fokker Aktiengesellschaft". Several Junkers designs were licensed to Fokker during this period. The visual similarity of Junkers and Fokker aircraft during the next decade, especially after Reinhold Platz adapted some of the Junkers design concepts, but mostly crafted in wood for the Fokker designs' wing structures instead of the all-metal