- Kriegsmarine and U-boat History: http://www.ubootwaffe.net/
- U-boats, commanding officers, ships attacked, U-boats surrendered, etc.: http://www.uboat.net/
- U-boat successes against aircraft: http://www.uboat.net/history/aircraft_losses.htm
- World War II logbooks (International Comprehensive Ocean-Atmosphere Data Set (ICOADS): http://icoads.noaa.gov/reclaim/pdf/20thC_British_logbooks_report_version_2009_2.pdf
