Fort Douaumont (French Fort de Douaumont) was the largest and highest fort on the ring of 19 large defensive forts protecting the city of Verdun, France since the 1890s. However, by 1915 the French General Staff had concluded that even the best-protected forts of Verdun could not resist bombardments from the German 420 mm (16.5 in) Gamma guns. These newly deployed giant howitzers had easily taken several large Belgian forts out of action in August 1914. As a result, Fort Douaumont and other Verdun forts, being judged ineffective, 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. The easy fall of Fort Douaumont, only three days after the beginning of the Battle of Verdun, produced a deep shock in the French Army. It set the stage for the rest of a battle which lasted nine months, at enormous human costs.