Inhalation is the usual route of entry.
Only HCN itself and the four cyanogen halides are likely to be of military interest. The cyanogen halides owe their toxicity to the CN-group, but the halogen moiety supplies them with their irritant properties. During World War I hydrogen cyanide and cyanogen chloride were used and cyanogen bromide to a limited extent. Hydrogen cyanide is a colorless, highly volatile liquid and represents a non-persistent hazard. It is highly soluble and stable in water.