Here's an interesting tidbit I found on deck gun attacks by U-35 during WWI. Commander Lothar von Arnauld de la Perière commanding.
U-35
U-23-class submarine. L/B/D: 212.2 × 20.7 × 11.5 (25.3 high) (64.7m × 6.3m × 3.5m/7.7m). Tons: 685/878 disp. Hull: steel. Comp.: 35. Arm.: 4 × 20TT; 1 × 8.8cm. Mach.: diesels/batteries, 2,000/1,200 ehp, 2 screws; 16.4/9.7 kts. Built: Friedrich Krupp AG Germaniawerft, Kiel, Germany; 1914.
On July 26, U-35 sailed from Cattaro and over the next 25 days sank 54 ships—more than any other submarine commander of any country in either of the two world wars—with an aggregate tonnage of more than 90,150 tons. The vast majority of these sinkings were in surface attacks, and in the course of the cruise, von Arnauld used only four torpedoes.
Gray, U-Boat War. Halpern, Naval War in the Mediterranean
CW
P.S. Extra tidbit: During his war time career, he fired only four torpedoes (one miss) and sank his victims (194 ships totalling 454,000 tons) always strictly according to prize rules with his boat's 88 mm deck gun.
Sea Classics May '04