It was followed by the two-engine Heinkel He 111 Doppel-Blitz, which became a mainstay of the Luftwaffe during World War II as a bomber. Heinkel's most important designers at this point were the twin Günter brothers, Siegfried and Walter, and Heinrich Hertel. The firm's headquarters was in Rostock later known as Heinkel-Nord (Heinkel-North), located in what used to be named the Rostock-Marienehe neighborhood (today's Rostock-Schmarl community, along the west bank of the Unterwarnow estuary), where the firm additionally possessed a factory airfield along the coastline in the Rostock/Schmarl neighborhood roughly three kilometers (1.9 miles) north-northwest of the main offices, with a second Heinkel-Süd engineering and manufacturing facility in Schwechat, Austria, after the Anschluss in 1938.