In discussing the work one can very well start with the Offense Section. This Section had two aims in view always, to develop methods of making the gases used by the Germans more economically than they were making them, and to develop better gases if possible. When we entered the war, chlorine, phosgene and chloropicrin were the lethal gases used, while bromoacetone and xylyl bromide were the lachrymators. It was not a difficult matter to prepare these. But the introduction of mustard gas in the summer of 1917 and of diphenylchloroarsine in the autumn of the same year, not only made our chemists ponder over a manufacturing method, but also so revised our notions of warfare that the possibility of using other substances created the need for extensive research. The development of bromobenzylcyanide by the French likewise opened a new field among lachrymatory substances. Colored rockets and smokes were developed for the Navy and Army. The smoke box was also studied but the work was taken over by the Pyrotechnic Section. A large amount of pure inorganic research on arsine and arsenides, fluorine, hydrofluoric acid and fluorides, cyanides, cyanogen sulfide and nitrogen tetroxide was carried out, sometimes successfully and at other times with little or no success. The Analytical Section not only carried out all routine analyses but developed methods for many new gases. The Offense Section worked in very close contact with the Small Scale Manufacturing Section (Chemical Production Section). Often it happened that a method, apparently successful in the laboratory, was of no value in the plant. Small scale plants were developed for mustard gas, hydrocyanic acid, cyanogen chloride, arsenic trichloride, arsenic trifluoride, magnesium arsenide, superpalite and bromobenzylcyanide. The Chemical Defense Section, organized January, 1918, was occupied with problems relating to protection, such as charcoal, soda-lime, and special absorbents, eyepieces, smoke filters, efficiency of absorbents, and special work with mustard gas. Charcoal demanded extensive research. Raw materials required a world-wide search, carbonizing methods had to be developed, and impregnating agents were thoroughly studied. This story is told in Chapter XIII. Soda-lime was likewise a difficult problem. Starting with the British formula, the influence of the various factors was studied and a balance between a number of desirable qualities, absorptive activity, capacity, hardness, resistance to abrasion, chemical stability, etc., obtained. The final product consisted of a mixture of lime, cement, kieselguhr, sodium permanganate and sodium hydroxide.