http://history-world.org/world_war_i_and_the_submarine.htm
http://www.revision-notes.co.uk/revision/927.html
http://www.worldwar1.com/stats
http://en.wikipedia.org/wiki/Technology_during_World_War_I
http://history-world.org/world_war_i_and_the_submarine.htm
http://www.revision-notes.co.uk/revision/927.html
http://www.worldwar1.com/stats
http://en.wikipedia.org/wiki/Technology_during_World_War_I