Chemical weapons in World War I volatile oily liquid. It was introduced as a vesicant by Germany in July 1917 prior to the Third Battle of Ypres. The Germans marked their shells yellow for mustard gas and green for chlorine and phosgene; hence they called the new gas "Yellow Cross". It was known to the British as "HS" ("Hun Stuff"), and the French called it "Yperite" (named after Ypres). Mustard gas is not an effective killing agent (though in high enough doses it is fatal) but can be used to harass and disable the enemy and pollute the battlefield. Delivered in artillery shells, mustard gas was
Opposing forces in the Polish September Campaign Poland successfully used 10 regular armoured trains against German forces, which were unprepared to face this kind of combat vehicle considered in 1939 so obsolete by German planners to be given any serious consideration. Although the trains proved indeed vulnerable to air attack, losses incurred against Polish trains ("Śmiały" Armored Train destroyed nearly 100 German tanks during the battles around Mokra village) convinced the Germans to reintroduce this type of vehicle into their own army after the September Campaign. Experience in the Polish-Soviet War (1919–1921), the only recent, major conflict the independent Second Polish Republic took part in, shaped Polish