25 Feb. 1916: The Germans captured Fort Douaumont at Verdun.

Unknown to the Germans, Fort Douaumont--the largest fortification in the Verdun sector--was manned by only a small maintenance crew led by a warrant officer. Only a couple of 75mm and 155mm guns remained in the complex and weren't manned. Additionally, the fort's remaining machine guns were packed in boxes. The decision to strip the large fortresses was made after the Germans used huge 420mm Krupp siege mortars to reduce the fortress system at Liège at the war's outset.

Following an initial probe of Douaumont's defenses by Brandenburg Regt. 24, a small detachment of about a hundred men managed to cut through barbed-wire obstacles in unobserved ditches and scale the top of the fortification, where they descended through maintenance entries and captured the few defenders.

Here, Germans of Brandenburg Regt. 24 fix bayonets in preparation for an assault on the flanks of Fort Douaumont.

For details, see: https://en.wikipedia.org/wiki/Battle_of_Verdun#Battle