Mustard gas
Mustard gas refers to a family of potentially lethal but primarily casualty-producing chemical weapons introduced in the First World War (WW1) and subsequently improved in World War II (WWII). The first version was impure dichloroethyl sulfide, code-named "Yellow Cross" by the Germans and "H" in the modern U.S. system. Originally produced by the Lowenstein reaction, it could be purified by distillation into the more potent "HD".
During WWII, the U.S. developed a family of much more toxic nitrogen mustards gasses, called the "HN" series. After their declassification at the end of the war, they proved to be the basis of some of the first effective antineoplastic agents for cancer chemotherapy.
World War I
While it had been synthesized in 1860, mustard gas was first used in warfare in September 1917. German forces employed it against Russians at Riga. Considerably more toxic by weight than earlier chemical weapons, it became a regular part of bombardments until the end of the war.
As opposed to other agents in use at that time, it could penetrate unbroken skin. A mask alone was insufficient protection. Its onset of toxic effects were usually delayed, so there was a terrifying sense of uncertainty after being shelled.
World War II
Both sides stockpiled mustard but did not use it, with the possible exception of the Japanese against the China. There was, however, a major mustard gas contamination incident in Bari, Italy when German aircraft unknowingly bombed an ammunition ship carrying the theater reserve of the agent.
Germany conducted the Nazi mustard gas experiments on concentration camp prisoners.