Military designers and the countries they work for have always sought to outdo one another on the battlefield, and creating massive artillery pieces has been no exception. Though there have been many extremely large artillery pieces manufactured, and some that are even larger than the ones listed here, these are the only ones that were actually used in combat.
1. Schwerer Gustav and Dora
The Schwerer Gustav and its sister gun Dora were the two largest artillery pieces every constructed in terms of overall weight (1350 tonnes) and weight of projectiles (15,700 pounds), while it's 800mm rounds are the largest ever fired in combat. The guns also had a range of over 24 miles. The guns were originally designed to be deployed against the French Maginot Line though the Blitzkrieg rendered that mission obsolete. Instead, the guns were deployed to the Eastern Front against the Soviet Union. The Schwerer Gustav entered combat during the German siege of Sevastopol in June 1942. The gun was manned by a crew of over 1400 men, 250 to assemble the weapon, two anti-aircraft battalions to protect it, and the rest to load and fire the weapon. Dora was set up to be deployed against Stalingrad, though it cannot be confirmed whether it fired against its target or not. Both guns remained on the Eastern Front but were not used in combat again. They were destroyed in Germany to avoid capture by the advancing allied armies.
Another product of Germany, the Karl-Gerät was a massive self-propelled mortar. Though it was capable of its own propulsion, its massive size made this an inconvenience, so it was usually disassembled and reassembled when it arrived at its firing position. The Karl-Gerät was designed as a siege weapon in particular to attack the Maginot Line. Its 21 man crew could fire a 600mm heavy bunker-busting shell nearly 3 miles at a rate of about 6 per hour. A total of 7 of these weapons were produced, one test piece and 6 others that saw extensive combat on both fronts. The Karl-Gerät made its combat debut when a 3 gun battery shelled the fortress at Brest-Litovsk during the opening phase of Operation Barbarossa in June 1941. The following year, a battery of Karl-Geräts took part in the siege of Sevastopol in June and July of 1942. Though it was planned for use in other operations on the Eastern Front, the threat of being captured by Soviet forces kept it out of the fight until 1944 when in August, one and then several other guns were sent to Warsaw to assist in quelling an on-going uprising against the German occupiers. The Karl-Gerät fired its last shots of the war during the Battle of Remagen in an attempt to destroy the Ludendorff Bridge.
3. Obusier de 520 modèle 1916
The Obusier de 520 was a railroad gun developed by the French during World War I. However, due to a delayed procurement process, the first gun did not reach trails until late 1917 during which a round exploded prematurely and destroyed it. The second gun was completed in 1918 but did not finish trails before the war ended after which it was put in storage. The Obusier de 520 modèle 1916 fired a 520mm round weighing over 3600 pounds to a range of over 8 miles. When Germany invaded France in 1940, the remaining gun was being renovated for battle where it was captured, still in the workshop, by the Germans. Germany, with a penchant for enormous artillery, pressed the Obusier de 520 into their own service where it participated in the siege of Leningrad in 1942 before also being destroyed by a round prematurely exploding in the barrel in January 1943.
4. Type 94 naval gun
The Japanese 18.1 inch naval gun was the largest gun ever to see combat at sea, being mounted on the Japanese Yamato-class battleships. The guns could fire a 1.5 ton shell over 26 miles and when mounted in their turrets, the entire piece weighed as much as a conventional destroyer of the time. Though the Yamato and Musashi were in operation for the entire war, neither used their Type 94 guns until near the time of their demise. Musashi's sole use of her Type 94's was in an anti-aircraft role, using the specially designed Sanshikidan "beehive" rounds attempting to stop the onslaught of American aircraft trying to sink her. She was unsuccessful and after taking 17 bomb hits and 19 torpedo strikes, she sank in October 1944. Also, during the Battle of Leyte Gulf, the Yamato used her guns for the only time in combat and sank the American escort carrier USS Gambier Bay before being forced to retire. The Yamato was finally sunk during the Battle of the Philippine Sea in April 1945.
5. BL 18 inch Mk I naval gun
The British 18 inch Mk I was originally designed and built during World War I, mounted on the HMS Furious. However, the Furious was converted during construction and two of its three turrets were emplaced on two Lord Clive-class monitors. Though the Mk I was slightly smaller than the later Japanese Type 94, its shell weighed more – 3320 pounds. The guns saw action very late in the war with the first bombarding a railway bridge in August 1918 while the other fired ahead of advancing troops in October 1918. A third gun was also built but did not see action during the war.
6. Big Bertha and Gamma Mörser
The Big Bertha and Gamma Mörser were both developments of a 420mm siege howitzer designed by Krupp for Germany leading up to World War I. Big Bertha was a mobile artillery piece while the Gamma had to be emplaced before firing, though they were moved by rail for operations in different areas. Both weapons fired a nearly 1 ton shell though the Gamma Mörser could fire the shell nearly 9 miles, a mile farther than the Big Bertha. Both types of weapons were deployed against Belgium during the opening stages of the Great War in 1914. Big Bertha guns were successful in destroying numerous forts in Belgium and France and gained a reputation on both sides for their power. The Gamma Mörsers were also used during destruction of the fort at Liege but due to their limited mobility did not see action again until the attack on Verdun in 1916. Most of the guns were destroyed or captured, though Krupp managed to hide one Gamma in a workshop. It survived to be repaired and used again during World War II where it saw action at the Siege of Sevastopol alongside other massive German artillery pieces.