Germany has commissioned over 1,500 U-boats (German: Unterseeboot) into its various navies from 1906 to the present day. The submarines have usually been designated with a U followed by a number, although World War I coastal submarines and coastal minelaying submarines used the UB and UC prefixes, respectively. When Germany resumed building submarines in the 1930s, the numbering of the submarines was restarted at 1. The renumbering was restarted at 1 a third time when Germany resumed building submarines in the 1960s.