This was the most successsful type of German midget submarine produced in this period. 39 feet long and propelled by a diesel/electric plant they had [when fitted with extra tanks] a range of 500 miles at 7kts. The special rudder made them highly manouvrable and depth charges had trouble sinking them, tending to throw them violently to one side. Over 300 were completed and several served in the French and Russian navies after the War.