the aircraft. It should be remembered that such aircraft are particularly vulnerable to rifle or machine gun bullets hitting and puncturing the container. A soldier with his steel helmet curtain, tippet, cape and impregnated suit and using his weapon should be able to face such an attack without serious losses. 6. Persistency of such contaminations. Persistency is naturally dependent upon many variable factors, but the following times apply to thickened mustard and represent the approximate periods during which liquid contamination is likely to persist, following low spray attack.