The 21 cm Mörser 99 (Abbr. 21 cm Mrs 99) was a German siege mortar built by Krupp which served during World War I. The mortar utilized a new nickel-steel alloy of greater strength than other cast cannons, though it lacked a recoil mechanism. While the gun was more effective than previous models, it was soon phased out because of improved field artillery and counter-battery fire, though it remained in service in limited numbers throughout the war because of heavy German losses. History Background The majority of military planners before the First World War were wedded to the concept of fighting an offensive war of rapid maneuver, which in a time before mechanization meant a focus on cavalry and light horse artillery firing shrapnel shells. Although the majority of combatants had heavy field artillery prior to the outbreak of the First World War, none had adequate numbers of heavy guns in service, nor had they foreseen the growing importance of heavy artillery once the Western Front stagnated and trench warfare set in. The theorists hadn't foreseen that trenches, barbed wire, and machine guns would rob them of the mobility they had been counting on, and like in the Franco-Prussian and Russo-Turkish wars the need for high-angle heavy artillery to deal with fortifications reasserted itself. Since aircraft of the period were not yet capable of carrying large diameter bombs, the burden of delivering heavy firepower fell on the artillery. The combatants scrambled to find anything that could fire a heavy shell, meant emptying fortresses and scouring depots for guns held in reserve. It also meant converting coastal artillery and naval guns to siege guns by either giving them simple field carriages or mounting the larger pieces on rail carriages. Service The Mrs 99 was designed in 1893 and built by Krupp in 1899. The Mrs 99 was a successor to earlier 21 cm mortars that had been in service since the Franco-Prussian War. The Mrs 99 was fairly conventional for its time and most nations had similar mortars such as the Mortier de 220 mm modèle 1880 or Mortaio da 210/8 D.S. However, its lack of recoil mechanism made it dated, and by the time the First World War broke out it had been largely made obsolete by the 21 cm Mörser 10. In 1914, it was estimated that 48 were in service with reserve units. However, it was brought back