During their trials the Type UB Is were found to be too small and too slow and had a reputation for being underpowered ; one commander compared his Type UB I to a " sewing machine " . According to authors R. H. Gibson and Maurice Prendergast in their 1931 book The German Submarine War , 1914 – 1918 , the UBs did not have enough power to chase down steamers while surfaced and lacked the endurance to spend any extended amount of time underwater , exhausting their batteries after little over an hour 's running . In @-@ service use revealed another problem : with a single propeller shaft / engine combination , if either component failed , the U @-@ boat was almost totally disabled .