any of several 420-millimetre (16.5-inch) howitzers that were used by advancing German forces to batter the Belgian forts at Liège and Namur in August 1914, at the start of World War I.

The guns were designed and built by the firm of Krupp (Krupp AG), Germany's largest armaments manufacturer, in the years before the war for the express purpose of overcoming modern forts built of reinforced concrete. The Big Berthas were the largest and most powerful artillery produced to that time. Each gun propelled a shell weighing 2,100 pounds (950 kg) for a distance of almost 9 miles (14 km). The shells were equipped with delayed-action fuses to explode after having penetrated a fortified target. The gun and its carriage, when fully assembled, weighed about 75 tons and was operated and serviced by a crew of about 280 men. For transport to the battlefield, the howitzer was disassembled into four sections—gun barrel, mounting, carriage, and ground platform—and loaded onto railway cars, which carried them to Belgium. After detraining, the sections were hauled by tractor-driven wagons to the firing sites and reassembled. Big Berthas and Austrian Skoda 305-millimetre howitzers were brought into action against the complex of Belgian forts around Liège on Aug. 12, 1914. They destroyed most of the forts in the next four days, thereby enabling the German army to sweep westward through southern Belgium on its way to invade northern France. Farther to the west, the forts around the city of Namur were similarly battered into surrender by Big Berthas and Skoda guns on August 21–25.

According to some sources, the nickname for the guns was bestowed by the Krupps in honour of Frau Bertha von Bohlen, head of the family. In popular usage, the name Big Bertha was also applied to the extreme long-range cannons with which the Germans shelled Paris in 1918, but these guns are more properly known as Paris Guns (Paris Gun).