These are lists of U-boats:
List of U-boats of Germany
List of U-boat types of Germany
List of U-boat regions of Germany during World War II
List of U-boat flotillas of Germany
List of U-boats never deployed of World War II Germany
Uncompleted U-boat projects of World War II Germany
List of successful U-boats of Germany for kill tonnage in World War I and World War II
Foreign U-boats of World War II Germany
List of Austro-Hungarian U-boats
