Although no chemical regiments were activated during World War II,
"There were at least eighteen chemical regiments in the Army’s inventory in the interwar period. …
Four regiments were allotted to the National Guard in 1931, but these were withdrawn in 1934 and allotted to the Organized Reserve.
Including the four regiments transferred from the National Guard, there were at least twelve Organized Reserve chemical regiments
(there may have been a 901st Chemical Regiment as well). Ten were standard chemical mortar regiments. The remaining two were intended
to perform duties as Chemical Warfare Service training regiments."
Source: Steven E. Clay, "US Army Order of Battle 1919–1941"
