http://mentalfloss.com/article/31882/12-technological-advancements-world-war-i
http://prezi.com/9qblqoc-jjht/medical-innovation-ww1/
http://www.firstworldwar.com/weaponry/machineguns.htm
http://www.uboat.net/wwi/
http://www.britannica.com/EBchecked/topic/612159/U-boat
http://en.wikipedia.org/wiki/History_of_agriculture_in_the_United_States#World_War_I
The text book
http://prezi.com/9qblqoc-jjht/medical-innovation-ww1/
http://www.firstworldwar.com/weaponry/machineguns.htm
http://www.uboat.net/wwi/
http://www.britannica.com/EBchecked/topic/612159/U-boat
http://en.wikipedia.org/wiki/History_of_agriculture_in_the_United_States#World_War_I
The text book