U-boat types of World War I Type Year of introduction Number of U-boats completed U 1 1906 1 U 2 1906 1 U-3 1907 2 U-5 1908 4 U 9 1908 4 U 13 1909 3 U-16 1909 1 U-17 1910 2 U-19 1910 4 U-23 1911 4 U-27 1912 4 U 31 1912 11 U-43 1914 8 U 51 1914 6 U 57 1914 6 U 63 1915 3 U 66 1913 5 U 81 1915 6 U 87 1915 6 U 93 1915 22 U 115 1916 0 U 127 1916 0 U 139 1916 3 U 142 1916 1 U 151 1916 7 UA 1912 1 UB I 1914 17 UB II 1915 30 UB III 1916 95 UC I 1914 15 UC II 1915 64 UC III 1916 16 UD 1 1918 0 UE I 1915 10 UE II 1916 9 UF 1918 0