During the start-up period of the institute the First World War broke out (July/August 1914) . This was to radically change the mission of the institute. It was put under military control and concentrated on research projects of immediate importance for the war effort. Thus, in 1914 during experiments involving explosives there was a serious explosion which claimed as its victim Otto Sackur, a very promising young physicist.

Fritz Haber himself offered his services to the War Ministry to carry out research on the supply of raw materials. He had recognized the significance of this subject for warfare very quickly, unlike the military leadership. Inspired by patriotism, Haber made also plans for the usage of chemical weapons. He directed their first large-scale application in 1915, believing that trench warfare could be terminated this way bringing the war to a quick conclusion, and in favor of Germany.

As the war continued the institute developed into a central research laboratory for the development of chemical weapons as well as for methods of protecting against chemical weapons. Haber's colleague and friend Richard Willstätter of the neighboring Kaiser-Wilhelm Institute for Chemistry developed at his request the respiratory filter for the gas mask. The institute was further extended by barrack buildings and started to occupy additional rooms of the other Kaiser-Wilhelm Institutes in Dahlem. During this time, many scientists (including Ferdinand Flury, James Franck, Herbert Freundlich, Otto Hahn, Reginald Oliver Herzog, Erich Regener, and Heinrich Wieland) were recruited to work on warfare-related projects, forming a staff of over 1,000 people.

At the end of the war Fritz Haber's military activities led the allies to label him as a "war criminal", because using chemical weapons was forbidden since the "The Hague Agreement about the Regulation of Land War" ("Haager Landkriegsordnung") of 1899 and 1907. However, this did not prevent the Swedish Academy of Sciences from awarding him the 1918 Nobel Prize for Chemistry. The final words from the presentation speech (June 1920) read (see http://www.nobel.se/chemistry/laureates/1918/ for more details):

"Geheimrat Professor Haber. This country's Academy of Sciences has awarded you the 1918 Nobel Prize for Chemistry in recognition of your great services in the solution of the problem of directly combining atmospheric nitrogen with hydrogen. A solution to this problem has been repeatedly attempted before, but you were the first to provide the industrial solution and thus to create an exceedingly important means of improving the standards of agriculture and the well-being of mankind. We congratulate you on this triumph in the service of your country and the whole of humanity. Please, accept now your prize from the President of the Nobel Foundation."