The German Army made heavy use of artillery during its march across Europe during World War 2 (1939-1945) and these systems generally fell into categories of light, medium, and heavy. One of their heavy implements became the 21cm Morser 18 series gun, a towed heavy howitzer providing long-range, hard-hitting indirect firepower against enemy positions. The weapon was adopted in the late 1930s as a successor to the outgoing 21cm Morser 16 units which debuted in World War 1 some decades before. Storied heavy guns manufacturer Krupp was charged with production of the new howitzer and over 700 units were eventually realized during a period spanning from 1939 to 1945.
The 21cm Morser 18 was typical of big gun designs of the period - requiring multiple crewmembers to operate efficiently, relying on separate-loading cased ammunition, and featuring a horizontal sliding breech block. The caliber was a hefty one at 210mm and its shells weighed 250 pounds apiece. Some six charges were fed into the gun tube to fire a single projectile and ranges were out to 15,840 yards (effective). The mounting hardware included a dual-recoil hydropneumatic mechanism - one of the first of its kind anywhere in the world - to keep the gun well-trained after subsequent firing. The dual-recoil arrangement meant that the gun and upper section of the carriage unit each recoiled in unison along separate recoil systems - providing for a very smooth firing action and also aiding repeat-fire accuracy. The gun's mounting hardware provided an elevation span of -6 to +70 degrees and traversal of 16 degrees from centerline.
The carriage system was a two-wheeled "box trail" design which allowed mover vehicles to tow the system to a new location at speed, typically on roads. To facilitate transportation of this massive weapon, the artillery piece could be broken down into two major sections - one made up of the all-important gun tube itself. The carriage also carried a gunnery platform along with it which, when the system was set in place with wheels raised, the platform could be turned a full 360-degrees to engage targets along any approach angle - providing a useful firing arc beyond the inherent 16 degree arc with the carriage wheels down.
Morser 18 guns were slow to get into the hands of frontline German troops after war was declared in September of 1939. This led to a limited production run as wartime artillery pieces went - manufacture of these big guns was actually halted in 1942 as the Army began settling in with the "smaller" 17cm Kanone 18 series guns during much of the early-war action (only about 340 of this series were made however). War time factors then forced production of Morser 18 guns to be restarted in 1943 and this continued on into the final months of the war - which ended in 1945.