In 1918 four of the surviving German boats were converted into coastal minelayers . Of the seventeen boats in German service , two were sold to Austria @-@ Hungary , one was sold to Bulgaria , and nine were lost during the war . One of the five Austro @-@ Hungarian boats was sunk and another mined and not repaired . The five surviving German boats , the four surviving Austro @-@ Hungarian boats , and the Bulgarian boat were all turned over to the Allies after the end of the war and were broken up .