Chemical, biological (CB) — and sometimes radiological — warfare agents were assigned what is termed a military symbol by the U.S. military until the American chemical and biological weapons programs were terminated (in 1990 and 1969, respectively). Military symbols applied to the CB agent fill, and not to the entire weapon. A chemical or biological weapon designation would be, for example, "Aero-14/B", which could be filled with GB, VX, TGB, or with a biological modification kit – OU, NU, UL, etc. A CB weapon is an integrated device of (1) agent, (2) dissemination means, and (3) delivery system.
Military symbols evolved out of the First World War from the British in part for secrecy, and to simplify reference to chemicals by something other than a chemical name. These symbols were sometimes applied as marking on weapons to indicate the agent contents. Military symbols constantly changed and had transitory definitions. For example, mustard gas was assigned the military symbol originally HS for "Hun Stuff". Later in the First World War the S in HS signified mustard gas that had about 25% solvent added to it. This was only in England, as HS was adopted as the military symbol by the United States – signifying crude mustard. In the Second World War the purity of mustard gas was improved through distillation, and this purified chemical warfare agent was designated HD. When it was mixed with a thickener (Agent VV), it was given the symbol HV. Today mustard gas is indicated by the single capital letter H, but HD is still in common use.
Military symbols can also reflect the name of where a chemical agent is manufactured. For example, chloropicrin has the symbol PS, which was derived from the British town in which it was manufactured during the First World War: Port Sunlight. Another device in assigning military symbols is in honor of the person that had devised the agent, such as Agent TZ (saxitoxin), which was derived after the name of its principal investigator, Dr. Edward Shantz.
Numbers are occasionally added to military symbols to reflect particular preparations. With riot control agents a 1 signifies micropulverized (e.g., CS1), and a 2 signified microencapsulated (e.g., CS2). With biological agents a 1 signifies a wet-type agent (e.g., UL1), and a 2 signifies a dry-type agent (e.g., UL2). Binary chemical weapons are signified by adding a 2, as in binary sarin (i.e., GB2).
Other formulations have their own designation. When the Tear Agent CS is formulated in a solvent it is signified by CSX. When agents are thickened with the addition of a polymer a T is usually added to the beginning of the symbol (e.g., thickened soman is TGD). The tear agent Mace, or Agent CN, had been formulated in several solvent forms, indicated by CNB (with benzene), CNC (with chloroform), and CNS (with chloropicrin and chloroform). Mixtures of agents have been identified with either a hyphen (e.g., CN-DM), or combining letters of the two agents (e.g., HD mixed with L is HL). Furthermore, one strain of the biological agent Tularemia has the symbol SR (lethal Schu strain), while another strain has JT (incapacitant 452 strain).
Military symbols for agents change from time to time for administrative reasons as well. To preserve secrecy, tularemia's symbol UL1 and UL2 was changed to TT and ZZ at one time, and then later to SR. During the Second World War cyanogen chloride's symbol was changed from CK to CC, but when it became apparent that CC marked munitions might be mistaken for CG (phosgene), the symbol was changed back.
The following designations are, or have been, used by the United States:
Material Testing Program EA (Edgewood Arsenal) numbers: