The Type "UB I" submarine (sometimes known as the UB-1" class"') was a class of small coastal submarines (U-boats) built in Germany at the beginning of the First World War. 20 boats were constructed, most of which went into service with the German Imperial Navy. Boats of this design were also operated by the Austro-Hungarian Navy (Kaiserliche und Königliche Kriegsmarine "or" K.u.K. Kriegsmarine) and the Bulgarian Navy. In the Austro-Hungarian Navy, it was called the '.