When the Second World War began, the Luftwaffe was one of the most technologically advanced air forces in the world. During the Polish Campaign that triggered the war, it established air superiority, and then air supremacy, quickly. It supported German Army (Heer) operations which ended the campaign in five weeks. The Luftwaffe's performance was as the Oberkommando der Luftwaffe had hoped. The Luftwaffe had rendered invaluable support to the army, mopping up pockets of resistance. Göring was delighted with the performance. Command and control problems were experienced, but owing to the flexibility and improvisation of both the army and Luftwaffe, these problems were solved. The Luftwaffe was to have in place a ground-to-air communication system, which played a vital role in the success of Fall Gelb.