One of the largest Tankers in the world at the time of her sinking, The French Tanker Emile Miguet was sunk by gunfire from the Famous U-48. A type VII B U-boat with of all things an 88 mm(roughly 3.5") gun! In fact, it was U-boat ace Herbert Shultze's biggest kill of the war!
"At 18.08 hours on 12 Oct, 1939, U-48 stopped the Emile Miguet, which was straggling from the convoy KJ-2 and shelled her until 19.00 hours. The tanker was set on fire, was abandoned and sank south-southwest of Ireland. The survivors were picked up by the American merchant Black Hawk."
http://uboat.net/boats/u48.htm