Task: Question Generation
Input (English): Regardless of the ability of the Luftwaffe to win air superiority, Adolf Hitler was frustrated that it was not happening quickly enough. With no sign of the RAF weakening, and Luftwaffe air fleets (Luftflotten) taking punishing losses, the OKL was keen for a change in strategy. To reduce losses further, a change in strategy was also favoured to take place at night, to give the bombers greater protection under cover of darkness.[b] On 4 September 1940, in a long address at the Sportspalast, Hitler declared: "And should the Royal Air Force drop two thousand, or three thousand [kilograms ...] then we will now drop [...] 300,000, 400,000, yes one million kilograms in a single night. And should they declare they will greatly increase their attacks on our cities, then we will erase their cities."
Output (English): In what year did Hitler give the speech at Sportspalast?