Above: An expensive Dictator mortar at the Siege of Petersburg, American Civil War, 1864.
Such weapons came with the promise of striking a knockout blow, but the very high protective factor of simple countermeasures, like trenches, negated most of the blast and debris danger (unless the trench was literally within the crater rupture zone radius). Huge quantities of munitions had to be fired, creating a war of attrition backed by constant supplies from an arms manufacturing industry. The facts about American Civil War countermeasures and thus almost certain defeat were not widely known so Germany ignored the American lessons of trench countermeasures in 1914, and therefore believed its big guns could strike a quick knockout blow. Trenches turned the planned short-duration war into a long-duration war of attrition, allowing a Naval blockade to defeat Germany. Germany faced exactly the same problem with its false expectation of using gas against trenches (gas masks were immediately improvised, as Herman Kahn explains in his 1960 On Thermonuclear War), and then submarines armed with torpedoes to try to achieve a Naval knockout blow or blockade of shipping against Britain. Germany submarines were simply detected with improvised ultrasonic-frequency hydrophones (waterproofed microphones, suspended underwater, were in 1918 supplemented with the asdic technique of sending out sonic waves to bounce back from submarines, and thus map their exact positions underwater, leading to the development of modern sonar), which allowed precise depth-charging to supplement the secret magnetic minefields guarding Naval bases and ports. German submarine action backfired completely when the Lusitania was torpedoed on 7 May 1915, causing America to enter the war. Ships subsequently sailed in convoys protected by anti-submarine warfare.
Modern machine guns and large caliber mortars failed to deliver their promised “knockout blow” in the American Civil War, but the lesson was ignored by Germany fifty years later in 1914, again in 1939, and continues to be ignored in virtually all media propaganda about all kinds of weapons today, despite the failure of the Nazi Blitz to defeat Britain, the failure of the first nuclear bomb dropped on Japan by itself to end World War II (the bomb on Hiroshima had to be followed by Nagasaki three days later, plus the Russian declaration of war, before Japan finally accepted a conditional surrender), and despite the failure of many megatons of explosives in aerial bombardment to knock out the North Vietcong, leading to American failure in the Vietnam War! The American Civil War was the first time in history that industrialized warfare was tried and it was blunted by simple improvised trench defenses to create a long-duration war of attrition, requiring the expenditure of vast quantities of ammunition and explosives in a failed effort to overcome very modest, low-cost defenses, as explained by Kenneth Macksey in his brilliant analysis, Technology in War: the Impact of Science on Weapon Development and Modern Battle (Arms and Armour Press, London, 1986, pp. 28-29):