The new aircraft were again able to challenge Allied aircraft, culminating in "Bloody April" during the Battle of Arras (9 April – 16 May 1917).[60] In the next two years, the Allied air forces gradually overwhelmed the Luftstreitkräfte in quality and quantity, until the Germans were only able to gain temporary control over small areas of the Western Front. When this tactic became untenable, development of new aircraft began, which led to the Fokker D.VII. The new aircraft created another "Fokker Scourge" in the summer of 1918 and as a condition of the Armistice, Germany was required to surrender all Fokker D.VII aircraft to the Allies.[61]