 The "Porpoise" class was the first class of operational submarines built for the Royal Navy after the end of the Second World War, and were designed to take advantage of experience gained by studying German Type XXI U-boats and British wartime experiments with the submarine , which was modified by streamlining and fitting a bigger battery.The "Porpoise"-class submarines were long overall and between perpendiculars, with a beam of and a draught of .Displacement was standard and full load surfaced and submerged.