When the war came Major Bauer was posted to the Operations Section of
Oberste Heeresleitung (OHL, Supreme Army Command) as head of Section II, which was responsible for heavy artillery, mortars, and fortresses. Earlier in 1914, the first of the Krupp
42cm mortars, nicknamed "Big Bertha", and its concrete-piercing shells were ready. They smashed the forts in Belgium and northern France. In 1915 the huge guns forced the surrender of the formidable Russian fortifications in Poland, like
Przemyśl, before dealing with the
Serbian strongholds at
Belgrade. For developing the mortars Bauer was awarded the
Pour le Mérite and an honorary doctorate from the University of Berlin. (In 1918 he received the Oak Leaves for his
Pour le Mérite. During the war he was awarded 25 German and foreign medals.) Before the war he had worked with the chemist
Fritz Haber to transform
nitrogen from the air into explosive precursors, which let the Germans make war despite the
Naval blockade of Germany preventing continued imports of supplies of nitrates that had come from Chile before the war. When the adversaries deadlocked in their trenches along the Western Front, Haber suggested that they could break through by releasing a cloud of poisonous chlorine gas, which is heavier than air. Bauer provided funds and scientists already in the army. Bauer, Haber and Duisberg, the head of the chemical cartel, and their horses were poisoned at the first field test; all were invalided for days. He was present at the first attack, which cleared the defenders out of miles of trenches defending the city of
Ypres, but was "heartbroken" because Supreme Commander
Erich von Falkenhayn had mounted only a diversionary attack, divulging their top-secret for almost no gain. Bauer continued to support the development of new gases, tactics to use them effectively despite protective masks, and Haber's mobilization of scientists for the war effort. Section II of
OHL Supreme Army Command carefully evaluated how their weapons performed on active service. For instance, in 1916 they produced a modified field gun that could be elevated to 40 degrees, compared to its former 16 degrees, and their light howitzer's range was increased 43 percent to . They formed a unit to develop assault tactics using
stormtroopers. Their first tank, introduced in May 1917, was too large and unwieldy, few were produced, so they had to use captured enemy tanks. Krupp and Daimler designed a light tank, but production was not authorized until French light tanks showed their value, consequently they could not be available until April 1919. Bauer strongly opposed Falkenhayn's plan to attack
Verdun in 1916 along a narrow front on the right bank of the Meuse, because their flank would be vulnerable to French artillery on the left bankhe was spot-on; before long they had to attack the left bank as well. While arranging artillery support before the attack he stayed at Fifth Army headquarters where he became a fast friend of its commander,
Crown Prince Wilhelm; they kept in touch thereafter. In the first salvo of the attack a 42 cm shell struck
Fort Douaumont, a key to the defense. It did not penetrate the reinforced concrete and sand layers: the Verdun forts were stouter than any the mortars had fired on hitherto. Later that year Bauer was dismayed by Falkenhayn's insistence along the
Somme front on packing infantry into the foremost trenches to repel the attacks, where they were chewed-up by the Entente's artillery preparations. Bauer decided that Falkenhayn must be replaced by his friend Ludendorff, who had displayed virtuosity on the Eastern Front. Supported by junior officers at OHL he tirelessly lobbied the highest echelons of the army and government against his superior, with criticisms of Falkenhayn like "...his decisions were half measures and he wavered even over these."{{cite book ==Total War==