240 mm howitzer M1 The 240 mm howitzer M1 , popularly nicknamed the " Black Dragon " , was a towed howitzer used by the United States Army . The 240 mm M1 was designed to replace the World War I era 240 mm Howitzer M1918 which was based on a 1911 French design and was outdated by World War II . The project to replace the M1918 began in 1941 . The 240 mm howitzer was the most powerful weapon deployed by US field artillery units during World War II , able to fire a high explosive projectile 25 , 225 yards ( 23 km ) . It was the largest field piece used by the US Army during the war except for naval ordnance adapted into railway gun s . The weapon addressed the requirement for super heavy field artillery capable of attacking heavily reinforced targets like those likely to be found along the West Wall . It was designed together with the longer ranged 8 inch Gun M1 and they both shared a related carriage . The 240 mm howitzer M1 proved very valuable against difficult targets such as heavy concrete fortifications . It , along with its super heavy artillery 8 inch gun design - mate saw considerable action during World War II in Europe . These weapons were also used in the Pacific campaign , notably in the Battle of Manila , but few targets justified the need for them . After World War II , the 240 mm howitzer was retained by the US army and deployed in the Korean War . It remained in US service until ammunition stocks were exhausted in the late 1950s . As of 2010 , the 240 mm howitzer M1 is still in service with the Republic of China Army , stationed in hardened bunkers of the frontline Kinmen and Matsu Islands . Service . The first operational use of the super heavy 240 mm Howitzer was by the U . S . 5th Army at the Anzio Beachhead in Italy in September 1943 . Its debut was an instant success , along with the gun ( which was deployed later at Anzio in April 1944 ) – super heavy artillery was used as counter - battery fire against German guns in their class . Their fire was accurate enough to not only knock enemy artillery out of action but also to destroy targets as small as German heavy tank s . US super heavy artillery also played a role in countering the infamous Anzio Annie railway gun and putting it out of action . In Italy , the 240 mm Howitzer was highly valued for its capability to destroy key bridges at long range . Army Ordnance officers credited the " devastating fire power and incredible accuracy " of the 240mm howitzer in playing a decisive role in the Italian Campaign . During the Battle of Monte Cassino , the weapon was used in the final destruction of the monastery at Monte Cassino already damaged by air attacks . In the Italian theater , a small number of the 240 mm howitzers also saw action in the service of the British Eighth Army . Despite of their initial misgivings over the deployment of such a heavy and unwieldy weapon , 5th Army commanders dubbed the 240 mm Howitzer as , " the most generally satisfactory weapon " in service in 1944 . The 240 mm howitzer would go on to see extensive service in the Western Front reducing reinforced targets requiring super heavy artillery . During the Korean war , twelve 240 mm howitzers were brought out of ' mothballs ' and sent to the front lines to deal with deep bunkers and fortifications built by the Chinese that could not be effectively attacked by smaller artillery weapons then on hand . They were utilized in two units in Korea , the 213th and 159th Field Artilleries . The weapons went into action on May 1 , 1953 . On that day , the first round was fired by Baker battery 213th at a target on top of a hill called ‘ the donut ’ by aerial observer s . The first round was just supposed to be a ceremonial shot , however it struck an ammo dump directly on top of ‘ the donut ’ which set off a chain reaction and blew part of the top of the hill off in a spectacular fashion . In the late 50s , several M1s were transferred to the Republic of China and stationed in the front line Kinmen and Matsu Islands . The guns were put on rails to enable the howitzers to deploy outside for fire missions and to retreat inside their hardened bunkers / tunnels for protection ( capable of withstanding direct hits from aerial bombs ) when needed . Self - propelled mount . A self - propelled version was made by mounted on a stretched Heavy Tank T26E3 chassis that had an extra bogie wheel per side as the T92 Howitzer Motor Carriage , but the war ended before it could be used and was later scrapped .