von Braun، Wernher؛ Ordway، Frederick I؛ Dooling, Jr.، David (1985) [1975]. Space Travel: A History. New York: Harper & Row. ص. 64, 69. ISBN:0-06-181898-4. NOTE: On February 21, 1931, the HW-I only climbed to 3 metres (Ordway & Sharpe, p18). NOTE: On March 13, 1931, Karl Poggensee launched a solid fuel rocket near Berlin to 1,500 ft altitude. NOTE: von Braun claims the VfR was founded in early June 1927 (the first issue of Die Rakete was dated "Januar-Juni 1927")
