On 1 September 1939, the Wehrmacht invaded Poland prompting the British Empire and France to declare war in her defence. Sperrle's "Luftflotte" 3 remained guarding German air space in western Germany and did not contribute to the German invasion, made possible by the non-aggression pact with the Soviet Union. The air fleet's Order of battle had been stripped of almost all of the combat units it held in March 1939. Only two reconnaissance staffel (squadrons) and a single bomber unit attached to Wekusta 51 remained. Sperrle received the competent Major General Maximilian Ritter von Pohl as his chief of staff. The two men made for a "good partnership". Sperrle was also assigned Major General Walter Surén, appointed as the air fleet's chief signals officer. Surén planned and organised the German field communications for the offensive in 1940. While guarding the Western Front during the Phoney War, Sperrle's small fleet of 306 aircraft—which included 33 obsolete Arado Ar 68s—fought off probing attacks of French and British aircraft.