Chemical mortar battalions were United States Army non-divisional units that were attached to infantry divisions during World War II. They were armed with 4.2-inch (107 mm) chemical mortars. For this reason they were also called the "Four-deucers".^[1]

In 1943, General Mark Clark's Fifth Army established a policy that no infantry division would be committed to combat without a chemical mortar battalion attached. As a result, when infantry units were rotated out of combat, the mortar battalions often stayed in the line and were attached to fresh units. Chemical mortars were in such high demand that often the companies of a battalion would be split up and assigned to different divisions. On the first day that General George S. Patton's Third Army became operational, in the summer of 1944, he issued a standing order to his staff that no infantry division would be committed to combat without a chemical mortar battalion attached, and no infantry regiment would be committed without a mortar company attached.^[2]

Mortars came to be acknowledged by U.S. Army commanders and personnel as being one of the most effective means of quickly striking at stationary targets, such as machine gun nests, prepared strongpoints, pillboxes and even artillery positions. Other advantages mortars offered compared to full-sized artillery pieces were their easier transportation, assembly, and disassembly. Thanks to their relatively small size, mortars were able to fire from concealed positions, such as natural escarpments on hillsides, or from woods.

The 4.2 in (107 mm) chemical mortar was developed from the British World War I-era 4 inch (101.6 mm) Stokes mortar. The Stokes mortar could fire twenty shells per minute and had a range of 1,100 yards (1,000 m) and in this way was capable of overwhelming enemy trenches. The American-built M1 4.2 inch (107 mm) mortar, first introduced in 1924, had a rifled barrel and a range of 2,300 yards (2,100 m). By the 1930s, after modifying the bore, improving the two-legged support and the recoil mechanism, and producing barrels made of seamless nickel steel, the M1A1 model was capable of sending shells 2,400 yards (2,200 m)

Chemical mortars were so named because of their original intent of firing poison gas, incendiary and smoke marker shells. Chemical shells were on standby during World War II, to be used in retaliation should the enemy employ chemical weapons first. By 1942, after authorization had been sought and granted to use high explosive shells, the new M2 model was produced with a stronger barrel. Its rate of fire was 40 rounds in the first two minutes, 100 rounds in the first 20 minutes and thereafter a sustained rate of 80 rounds per hour. These variations were caused by the stresses and strains on the barrels and the rest of firing mechanisms that were being imposed by different firing conditions.

Later, the mortar was developed to be capable of firing shells from a mere 565 yards (517 m) at minimum propellant charge, to a range of 4,400 yards (4,000 m). The propellant charges were manufactured as square disks with a hole in the middle, strung together, fitted into cartridges, and sewn together into bundles of various thicknesses. The rifled barrel gave the mortar remarkable accuracy; fire was often called on targets within fifty yards of friendly positions. The low-velocity shells were totally silent in transit and gave no warning of their powerful explosions (the M2 mortar's M3 high explosive shell contained 3.64 kilograms (8.0 lb) of explosives, placing it midway between the 2.18 kilograms (4.8 lb) of the 105 mm howitzer M2A1's M1 shell and the 6.88 kilograms (15.2 lb) of the 155 mm howitzer M1's M102 shell), which tended to create panic among enemy forces who were unexpectedly subjected to their firepower. The mortar was called the "grass-cutter" by German troops because its high explosive shell exploded and fragmented just a few inches above ground level. The mortars often fired white phosphorus munitions (WP) shells to block enemy observation with smoke; white phosphorus also caused casualties and fires, being especially effective against dug-in troops because the burning particles arced upward and fell directly down into foxholes.^[3]

Chemical mortar battalions had their origins in gas regiments, which were first organized in the interwar period. They were redesignated chemical regiments in 1929. The 1st and 2nd Gas Regiments were allotted to the Regular Army. The 1st Gas Regiment had seen service in World War I. It was inactivated on 15 April 1935 and concurrently reorganized entirely with Organized Reserve personnel as a Regular Army Inactive unit. It was inactivated on 9 October 1940 at Philadelphia, Pennsylvania, by transfer of personnel to the 902nd Chemical Regiment. The 2nd Chemical Regiment was constituted in the Regular Army 1 April 1931, assigned to the Zone of the Interior, and allotted to the Fourth Corps Area. Company C, the only active unit, was organized 1 April 1931 at Fort Benning, Georgia, from Company D, 1st Chemical Regiment. The remainder of the regiment was organized in June 1932 with Organized Reserve personnel as a Regular Army Inactive unit at Columbus, Georgia. It was inactivated on 25 August 1940 at Columbus by relief of personnel.

There were two separate Regular Army chemical battalions, one animal-drawn and one motorized. The animal-drawn 1st Chemical Battalion was located in Hawaii due to the mountainous terrain there. Company A, the only active unit, was organized 4 March 1931 at Schofield Barracks from the 2nd Separate Chemical Company. It was disbanded on 12 March 1942. The 2nd Chemical Battalion was organized on 16 April 1935, less Companies B and C, at Edgewood Arsenal, Maryland, and performed duties as the support unit for the Chemical Warfare School. Companies B and C were allotted to the Third Corps Area as inactive units and organized with Organized Reserve personnel.

Four chemical regiments (the 101st-104th) were allotted to the National Guard in 1931, but these were never organized and were withdrawn from the National Guard in 1934 and allotted to the Organized Reserve as the 307th-310th Chemical Regiments. The headquarters of the 307th, 308th, and 310th Chemical Regiments were initiated in 1937, but the 309th Chemical Regiment was never initiated. All the regiments were disbanded on 18 October 1943. The 301st and 302nd Gas Regiments were constituted and initiated in the Organized Reserve in 1923, while the 303rd-306th Chemical Regiments were initiated in 1931. All the regiments were disbanded on 18 October 1943. The 902nd and 904th Chemical Regiments were constituted in the Organized Reserve in 1940 and intended to be used as support units for the Chemical Warfare School, but they were both inactivated by relief of personnel on 7 August 1941.^[4]

Originally, chemical mortar battalions had 36 officers, one warrant officer, and 973 enlisted men, for a total of 1,010, distributed among a headquarters, headquarters company, medical detachment, and four mortar companies. Each mortar company had twelve mortars organized into two platoons, each with two sections, with each section having three squads of one mortar each. Sidearms for battalion members included 820 M1911 pistols. There were 88 2.5-ton trucks and 36 various smaller vehicles.^[19] In actual combat, the 2.5 ton truck assigned as a prime mover often proved too conspicuous, so mortar crews sometimes used jeeps or mules to transport the mortar parts.^[20]

In July 1944, the 84th Chemical Mortar Battalion in Italy reorganized under the "long ignored" table of organization of September 1943. Lieutenant Colonel Ronald LeV. Martin of the 92nd Chemical Mortar Battalion received permission to eliminate one company of his battalion, anticipating future developments. In mid-1944, the War Department again revised the table of organization based upon the recommendations of Chemical Warfare Service officers with combat experience. One mortar company was eliminated to better fit with the three infantry regiments of the "triangular" infantry division, and the mortar companies were reorganized to have three platoons of four mortars each instead of two platoons of six mortars each. The strength of the battalion rose from 622 to 672, mainly because of the redesignation of the headquarters detachment of 63 men as a headquarters company with 155 men.^[21] Per Table of Organization and Equipment 3-25 of 29 September 1944, a typical chemical mortar battalion had an establishment of 37 officers, 138 NCOs and 481 junior enlisted men not counting the attached medical detachment. It consisted of:

• 1 chemical mortar battalion headquarters company, containing:
  • 1 company headquarters section (4 officers, 4 noncommissioned officers, and 14 junior enlisted men)
  • 1 battalion headquarters section (5 officers, 6 noncommissioned officers, and 20 junior enlisted men
  • 1 maintenance section (1 officer, 2 noncommissioned officers, and 6 junior enlisted men)
  • 3 ammunition sections (each of 2 noncommissioned officers and 29 junior enlisted men)
• 3 chemical mortar companies
• Attached medical detachment (1 officer, 1 noncommissioned officer, and 13 junior enlisted men)

A chemical mortar company usually had an establishment of 9 officers, 40 noncommissioned officers and 118 junior enlisted men. It consisted of:

• 1 chemical mortar company headquarters section (three officers, seven noncommissioned officers, and 28 junior enlisted men)
• 3 mortar platoons

A mortar platoon consisted of:

• One platoon headquarters (two officers, three noncommissioned officers, and six junior enlisted men)
• Four mortar squads, each of which had one squad leader, (noncommissioned officer) one gunner, (noncommissioned officer) one assistant gunner, (junior enlisted man) three ammunition bearers, (junior enlisted men) and two truck drivers (junior enlisted men)

^[22]

In November 1944, the 84th and 100th Chemical Mortar Battalions stationed in Italy reorganized under the table of organization of September 1944. Beginning in December 1944 and continuing into spring 1945, battalions in Europe reorganized under the new table of organization.^[23]