The concept of the mortar dates from the 15th century, although no exact date of invention is known. An early mortar was a large musket loaded gun, differing in one important respect. To be called a mortar it must fire at an angle of more than 45 degrees from the horizontal. However, early development was slow, and they did not begin to resemble the modern versions until the early 20th century. In 1915 came the invention of the Stokes mortar, which is widely regarded to be the forerunner of many weapons in use today.
In general, a mortar is a large gun with a smooth bore barrel, typically around five or six feet long, which discharges finned bombs. Most are mounted onto a baseplate with two wheels, and a tripod or bipod to enable it to be pointed upwards at the correct angle. The bomb has fins on its tail to give stability in flight. In the tail is a powder cartridge, with auxiliary charges clipped around the fins. To fire a shot, a bomb is dropped into the barrel, hitting a fixed firing pin at the bottom. This strikes an ignition cartridge, which detonates the auxiliary charges, causing an explosion which propels the bomb towards the target. The bomb then follows an arching trajectory, dropping almost vertically when it detonates. This vertical descent gives the mortar an advantage over the conventional artillery shell, because the effects of the blast are felt in all directions.
Modern mortars vary in efficiency and range, but with a few exceptions are similar in appearance and calibre (typically 81 or 82 mm calibre and 8 or 9 km range). Variations include rocket boosted mortars and those modified to fit onto armoured personnel carriers and tanks.
