U-boat Campaign (World War I) - Summary - Allied and Neutral Tonnage sunk by submarines in World War I

Reference 1: January, February, March, April, May, June, July, August, September, October, November, December and Total.

Reference 2: 1914, 1915, 1916, 1917 and 1918.

Source: http://en.wikipedia.org/wiki/U-boat_Campaign_(World_War_I)