Chemical Mortar Battalions in Combat
In the late 1930s and early 1940s, memories of toxic chemical warfare were fresh in the minds of both civilians and the military, and the U.S. Chemical Warfare Service (CWS) received significant funding to prepare. Methods for delivering toxic chemicals included landmines, bombs, spray tanks, artillery shells and more, but one of the most essential methods was expected to be heavy mortars. With their high-arching trajectory, mortars could provide critical support for infantry troops in rugged terrain and within the intermediate range that was too close for artillery and too far for grenades and other hand-held weapons. The U.S. “4.2-inch chemical mortar” was designed to fire shells filled with mustard agent, phosgene, phosphorous, or smoke. It was rifled to achieve very high accuracy, and it also gave impressive performance in terms of range, accuracy, rate of fire, mobility, and the quantity of toxin it could deliver per shell. Germany and Japan also had heavy mortars that could fire toxic shells, and each nation also had its own stockpiles of poisonous shells.
On December 7th, 1941, the U.S. Army had received only 44 of these new mortars, 32 of which had been shipped to Hawaii. The head of the Hawaiian Department of the CWS, Lt. Col. George Unmacht, made immediate preparations to use the chemical mortars, defending Hawaii’s beaches against what he and many others expected to be imminent waves of Japanese infantry landing on Hawaiian beaches. Given the well-known history of the previous World War and Japan’s recent history of using toxic chemicals in China, there was good reason to expect Japanese troops invading Hawaii would come ashore behind clouds of poison gas. The Japanese infantry never landed in Hawaii, and Japan never used toxic gases against Americans. Preparation for gas warfare continued on all sides, however, and it included American manufacture of 549,000 mustard-filled shells and 49,000 phosgene-filled shells specifically for its 4.2-inch mortars.
None of these mustard or phosgene shells was ever fired in combat, but tests soon revealed that the 4.2-inch (107 mm) chemical mortars were just as effective in firing high-explosive rounds as they were in delivering chemicals. During early fighting in North Africa, German 120-mm mortars out-gunned the smooth-bore 60-mm and 81-mm mortars of American infantry, and the chemical mortars of the CWS offered a quick alternative. Soldiers in chemical mortar battalions were still members of the CWS (which was usually a service branch, not a combat branch). Still, the equipment authorized for up to 1000 men in each mortar battalion demonstrates they were designed to be a formidable fighting force. In addition to 48 mortars, a chemical mortar battalion generally had 450 carbines, 150 Garand rifles, 15 heavy machine guns, and 23 anti-tank rocket launchers. By the end of the war, the Chemical Warfare Service had deployed 25 chemical mortar battalions and two separate chemical mortar companies, providing close support for infantry in Europe, Asia and the Pacific.
The first tactical success for CWS mortar battalions came on July 9, 1943, during the first hours of the assault on Sicily. The 2nd, 3rd, and 83rd Chemical Mortar Battalions quickly proved their value, for example, when they forced enemy tanks to move back from the American line to where the Army’s heavy artillery and naval guns could do their work. The mortar battalions also proved they could each maintain an average rate of fire of almost 100 rounds per hour for many hours. Their value on Sicily placed the chemical mortar battalions in high demand for the fighting which followed in Italy, where their ability to move quickly in rough terrain added further to their popularity with infantry troops and commanders.
On D-Day, June 6, 1944, the 87th Chemical Mortar Battalion went ashore during the first hour of the landing on Utah Beach and quickly began to fire rounds over the cliffs above. The 87th paid a heavy price, with a total of 84 men killed in action during the unit's 16 months overseas. Like the CWS as a whole, the 87th and the other three chemical mortar battalions who fought in Normandy fired only high-explosive, smoke and phosphorus shells, never the toxic chemicals for which their mortars were initially designed. Both America and Germany had large inventories of heavy mortars and toxic chemical shells for those mortars. Especially on D-Day, many military strategists expected Germany to use its toxic munitions in an all-out effort to drive the Allies back off the beaches. The soldiers of the 87th certainly had the equipment and the skill needed to “respond in kind” (as Roosevelt had promised) to Axis use of toxic munitions. It is not clear how close mustard- and phosgene-filled shells were to the soldiers shown firing high-explosives in the photo. There should be little doubt, however, that the Americans had a plan to begin firing the complete set of 4.2-inch munitions America had produced, if Germany had initiated chemical warfare and if Roosevelt had authorized an American chemical response.
In Europe, the CWS generally provided one chemical mortar battalion to support each infantry division. In the Pacific, fewer mortar battalions were available, and these were often split. In one example, three companies from the 82nd Chemical Mortar Battalion supported the 37th and Americal Divisions almost continuously from February through August 1944 during the “Battle of the Perimeter” on Bougainville. The difficulty in seeing enemy targets in jungle terrain inspired new methods. During one 19-day period in March 1944, the three chemical mortar companies fired 35,000 mortar rounds, many to help repel Japanese night attacks. The consistent precision of the 4.2-inch mortars was particularly important as the CWS mortarmen “walked” their high-explosive shells (each with a lateral impact of 10 yards) so the shells landed within 25 yards of friendly troops.
Like America and Germany, Japan had its own heavy mortars capable of firing shells filled with toxic chemicals, but never used them after America entered the war. All three nations ended the war with a significant quantity of unused chemicals and toxin-filled shells, some of which continue to present their own environmental and health challenges. It is important to note that the only major uses of toxic chemicals during WWII were by Japan in China and by Germany in its extermination camps. No nation used toxic chemicals against an enemy that could retaliate in kind. We owe an enormous debt to the soldiers who served in CWS mortar units for their contributions in “conventional” warfare. We also owe recognition to them and the entire CWS for maintaining the chemical deterrent that stopped Germany and Japan from using their chemical munitions.
A detailed account of the 86th Chemical Mortar Battalion is available online at https://86thchemical.us/history-of-the-86th-chemical-mortar-battalion/. The 86th arrived in Normandy on June 29, 1944, and was in combat for 315 days. Other sources include The Chemical Warfare Service in World War II (published in 1948) and The Chemical Warfare Service: From Laboratory to Field (published in 1988).