 Complete the following phrase:  As the German ground forces advanced across the Ukraine in August and September, the air units of JG 52 kept pace  constantly moving on to forward airbases. The Gruppe was involved in providing cover for the southern crossings over the Dnieper, the capture of Poltava, the First Battle of Kharkov and then crossing the Perekop isthmus into the Crimea. They often flew three or four missions a day when weather permitted. By the end of October Graf was mastering his flying technique, becoming adept at low-level flying, and had achieved 20 victories. The rains arrived in November, turning the airfields to mud and limiting air operations and the number of serviceable aircraft. Grafs unit was moved forward to Taganrog to support the 