Ethyldichloroarsine
Ethyldichloroarsine, sometimes abbreviated "ED" and also known as ethyl Dick, is an organoarsenic compound with the formula CH3CH2AsCl2. This colourless volatile liquid is a highly toxic obsolete vesicant or blister agent that was used during World War I in chemical warfare. The molecule is pyramidal with the Cl-As-Cl and C-As-Cl angles approaching 90° (see image). Ethyldichloroarsine has high chronic toxicity, similar to lewisite. References 

Arsenical vesicants
Organoarsenic chlorides