 The <unk> of the boats consisted of a single propeller shaft driven by a <unk> ( Germaniawerft ) or <unk> ( <unk> ) diesel engine on the surface , or a <unk> @-@ <unk> electric motor for underwater travel . The <unk> boats were capable of nearly 7 @.@ 5 knots ( 13 @.@ 9 km / h ; 8 @.@ 6 mph ) on the surface and a little more than 6 knots ( 11 km / h ; 6 @.@ 9 mph ) submerged . The Germaniawerft boats were about 1 knot ( 1 @.@ 9 km / h ; 1 @.@ 2 mph ) slower than their <unk> @-@ made counterparts . The boats were equipped with two 45 @-@ <unk> ( 17 @.@ 7 in ) bow torpedo tubes and carried two torpedoes . They were also armed with a single 8 @-@ millimetre ( 0 @.@ 31 in ) machine gun affixed to the deck . 
