Arsine.

This is coolbert:

"6. The German Commandatura used small amounts of colourless and odourless gas on the MAGINOT LINE and at LIEGE. A medical man who has been treating soldiers suggests that this gas was of the arsine type." [as extracted from a Soviet secret message dated 1940, PRESS REPORTS ABOUT THE  LUFTWAFFE AND USE OF GAS IN FRANCE (1940)].

"The Arsine Scare of October 1939 and the EA Container"

Elements within the EA British container filtering poison gases. Life of troop wearing the respirator saved.

Gas mask filters [EA container] of the period found to be hardly effective against the arsine form of poison gas. Arsine a choking agent 

"In October 1939, based on research undertaken on a recovered German Respirator, it was discovered that British Type E Containers [filtration] were around 10x more susceptible to the effects of Arsine Gas. This suggested to scientists that the Germans must have been planning to use this gas."

GREAT WAS THE FRIGHT FROM POISON GAS ATTACK ON BOTH TROOPS AND CIVILIANS IN THOSE DAYS IMMEDIATE TO THE SECOND WORLD WAR.

No such poison gas attacks by the Germans during World War Two? For reasons not properly or fully explained? Even though the German possessing Tabun, a nerve agent for which neither the allies or Soviets had protective respirator filters.

The Japanese of course making extensive use of chemical munitions during the Second Sino-Japanese War of 1937-1941. Hirohito himself [?] authorizing use of such weapons. Also the Italians make use of such weapons during their campaign to subdue Ethiopia [called Abyssinia at the time].

coolbert.