Austro-Hungarian Navy
A total of 20 Type UB I submarines were built, 17 for the German Imperial Navy and three for the Austro-Hungarian Navy. Two of the German submarines—"UB-1" and "UB-15"—were sold to Austria-Hungary and commissioned into the Austro-Hungarian Navy as "U-10" and "U-11", respectively. Those two and a further three built by AG Weser comprised the virtually identical "U-10" class for the Austro-Hungarian Navy. Another of the German submarines, "UB-8", was sold to Bulgaria in May 1916, becoming "Podvodnik No. 18".