Gerken, Louis (1989). Torpedo Technology (Illustrated ed.). United States: Pennsylvania State University. p. 57. ISBN978-0961716325. Retrieved 30 June 2017.
Marc Buggeln. "Neuengamme / Bremen-Farge". Holocaust Encyclopedia. United States Holocaust Memorial Museum. Retrieved 29 January 2011.
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Jones, Marcus O. (2014) "Innovation for Its Own Sake: The Type XXI U-boat", Naval War College Review, Vol. 67, No. 2, Article 9 https://digital-commons.usnwc.edu/nwc-review/vol67/iss2/9%7C[permanent dead link] p10 "Early Type XXI hulls suffered from defective diesel-engine superchargers, faulty hydraulic torpedo-loading systems, trouble-prone steering systems..."