Fort Douaumont () was the largest and highest fort on the ring of 19 large defensive works which had protected the city of Verdun, France, since the 1890s. By 1915, the French General Staff had concluded that even the best-protected forts of Verdun could not withstand bombardments from the German 420 mm (16.5 in) Gamma guns. These new super-heavy howitzers had easily taken several large Belgian forts out of action in August 1914. Fort Douaumont and other Verdun forts were judged ineffective and had been partly disarmed and left virtually undefended since 1915. On 25 February 1916, Fort Douaumont was entered and occupied without a fight by a small German raiding party comprising only 19 officers and 79 men, entering via an open window by the moat. The easy fall of Fort Douaumont, only three days after the beginning of the Battle of Verdun, shocked the French Army. It set the stage for the rest of a battle which lasted nine months, at enormous human cost. Douaumont was finally recaptured by three infantry divisions of the Second Army, during the First Offensive Battle of Verdun on 24 October 1916. This event brought closure to the battle in 1916. History Construction work started in 1885 near the village of Douaumont, on some of the highest ground in the area and the fort was continually reinforced until 1913. It has a total surface area of and is approximately long, with two subterranean levels protected by a steel reinforced concrete roof thick resting on a sand cushion. These improvements had been completed by 1903. The entrance to the fort was at the rear. Two main tunnels ran east–west, one above the other, with barrack rooms and corridors to outlying parts of the fort branched off of the main tunnels. The fort was equipped with numerous armed posts, a 155 mm rotating/retractable gun turret, a 75 mm gun rotating/retractable gun turret, four other 75 mm guns in flanking "Bourges Casemates" that swept the intervals and several machine-gun turrets. Entry into the moat around the fort was interdicted by Hotchkiss anti-personnel revolving cannons located in wall casemates or "Coffres" present at each corner. With hindsight, Douaumont was much better prepared to withstand the heaviest bombardments than the Belgian forts that had been crushed by German Gamma howitzers in 1914. The German invasion of Belgium in 1914 had forced military planners to radically rethink the utility