The 4.2 inch M2 mortar was a rifled muzzle-loading weapon designed for high-angle fire. Because of its size and weight, the weapon was used as Regimental artillery, often vehicle mounted.
The M2 mortar consisted of the M2 barrel (48 inches long, 105 lb.), the M2A1 base plate (175 lb.) and the M1 elevating standard (53 lb.) for a total weight of 333 pounds. The 4.2 inch mortar first saw action with the 2nd/3rd Chemical Mortar Battalions in the invasion of Sicily 9 July-17 August 1943. This large weapon was used by "four-deucers" in 25 Chemical Mortar Battalions during World War II, and in the Korean War by one unit. The photo above to the left shows a 4.2 inch chemical mortar demonstration at Edgewood Arsenal, MD, June 1942.
The 4.2 inch M2 was replaced by the even heavier M-30 mortar. Issued to US forces beginning in 1951, the M30 served in Korea gradually replacing the M2 which also saw duty in Korea. The M30 provided heavy mortar support for ground operations in Vietnam.
The M30 had a circular baseplate and greater range. It weighed 626 pounds including the tube, base ring, supporting standard, and other components. It could bring fire to a range up to 6,500 yards (meters). Manuals include FM 23-92 "4.2-inch Mortar, M30" and TM 9-261A "4.2-inch Mortar M30 (T104) and 4.2-inch Mortar Mount M24 (T61)" dated May 1951 or later.
The M2 and M30 4.2 inch mortars had rifled tubes that stabilized the flight of its rounds by imparting a spin, like a rifle barrel. All other U.S. mortars fired fin-stabilized ammunition because they had smooth-bore tubes.
M120 120mm Mortar
The M30 4.2inch Mortar was phased out of U.S. service starting in 1991, replaced by the NATO-standard M120 120mm Mortar. This 120mm system includes the weapon, the fire control systems, the ammunition. When carrier-mounted in the M1064A3 (based on an M113A3 track, photo right) the M120 is denoted as the M121. The M120 ground emplaced system is transported by the M1100 trailer.
The M120 mortar, used by mechanized infantry, armor and cavalry units, increases range, lethality, illumination and smoke screening effectiveness over the M30 mortar it replaces. The M120 has a tube length of 69 in (1.75 m) and a range from 200 meters to 7,240 meters. It weighs 319 pounds.
Find More Information on the Internet
There are many fine websites that have additional information on this
topic, too many to list here and too many to keep up with as they come and go.
Use this Google web search form to get an up to date report of what's out there.
For good results, try entering this: mortar 4.2 inch or 120mm. Then click the Search button.