4.2" Chemical Mortar Platoon (Mid & Late War)
(US711)
Contains: 1 command team (3 miniatures, 1 Observer team (2 miniatures), 4 4.2" Mortars, 16 crew, 2 small and 4 large bases.
The 4.2" mortar was descended from the Stokes mortar of the WWI British Army. The First Gas Regiment of the US Army Chemical Warfare Service (CWS) obtained Stokes mortars from the British in 1918 and employed them along the western front. In July 1918, the Army contracted with American firms for the manufacture of these mortars. After some experimentation with improving on the Stokes Mortar design by adding stabilising fins, increasing the propellent charge and rifling the barrel, moves were made to design a indigenous chemical mortar. By June 1924, one of the experimental barrels could send shells through the air on accurate, spin-stabilized flights of almost 2300 yards. Adoption of a rifled barrel meant the engineers had to redesign several components of the mortar, from baseplate to shell fuse. Previous mortar shell fuses had all-ways fuses to make certain that the tumbling shell would explode no matter whether it landed on its base, side or nose. Fuses of this type could not be used on a spinning shell since centrifugal force would activate the fuse and cause the shell to burst as it left the muzzle of the mortar. After considerable experimentation, engineers developed a safe, dependable fuse that could be set for impact or time. Vanes were added to the inside of chemical shells to prevent the liquid fillings, such as mustard or phosgene, from surging around inside the shell, unbalancing it and causing it to tumble and yaw in flight. To seal the bore against loss of explosion gases, and to force the shell to conform to the rifling an ingenious solution was devised. A driving mechanism at the base of the projectile consisted of two round plates, one of brass and one of steel. The brass disk was designed so that its edge could be forced outward by pressure. When the powder exploded, gas pressure rammed the steel plate up against the softer brass plate, forcing its edge out and into the grooves, sealing gases in and forcing the shell to spiral out of the barrel.
Because of the increased recoil of the new mortar an all steel baseplate was designed to replace wooden one of the original Stokes mortar. In 1928 the model M1 4.2" chemical mortar entered service.
During the next decade CWS engineers put considerable thought into improving the standard model. The two-legged support was strengthened; barrels were made specifically for the new model from seamless drawn-nickel steel tubing. A spring shock absorber was placed on the barrel to prevent the force of recoil from breaking the connection between support and the barrel. After seven years of work, the CWS completed a greatly improved mortar, model M1A1, with a range of 2400 yards. The next step in the development of the mortar came about as a result of an addition to the mission of CWS troops. Though it was initially intended as a chemical weapons delivery system, the general non-deployment of these weapons meant it’s role in combat became more one of a heavy mortar firing smoke and high-explosive shells. In April 1942 the Chemical troops were given permission to use high explosive ammunition in the mortar. This gave the CWS impetus in lengthening the range of the 4.2” mortar.
Engineers started working on solutions immediately. Tests demonstrated that simply adding 50% more powder to the propellent increased the range by 800 yards to a total of 3200 yards.
This was quickly adopted. The barrel and baseplate were strengthened to cope with the higher explosion pressure. The modified mortar became the M2. The CWS carried the M2 into the war. The 4.2" mortar first saw action [with the 2nd and 3rd Chemical Mortar Battalions] in Sicily in the summer of 1943. Mortar squads were among the first waves of troops to hit the beach, and they were in action a few minutes after landing. During the 38-day campaign, they shot 35,000 rounds of ammunition in crash concentration, harassing, interdictory and counter-battery fire, and in tactical smoke screening missions. The mortar made an excellent impression on commanders of Infantry, Ranger, Armored and Airborne units. Thereafter there was no question that the CWS had taken the right course in turning the chemical mortar into a HE-delivering weapon.
15mm, metal
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