Geneva Protocol on gas warfare was signed in 1925. Whether such stocks were actually acquired is still not clear. New Zealand actively supported retention of the 'right' of chemical retaliation when the question of banning CW entirely was raised at the 1932 Disarmament Conference.
During World War 2 New Zealand was involved in research, development and production of CW weaponry.
New Zealand acquired a considerable quantity of chemical weapons. One stockpile may have accompanied the 3rd Division to the Pacific. The other main stockpile was stored at Belmont between 1942 and 1946, and included 12 770 rounds of 25 pounder mustard shell, 15 300 gas bombs for 4.2 inch mortar.
The ultimate fate of this CW arsenal is not clear. Some may have been transferred to US forces in the Pacific.
In 1946 some 1500 tons of 25 pounder shells and 20 tons of mortar bombs were dumped off Cape Palliser. This would be equal to about 135,000 shells and 2200 gas bombs. A further 200 tons were dumped in Hauraki Gulf. Other gas munitions may have been dumped as late as 1957. RNZN ships apparently continue to carry tear gas munitions for riot control operations ‘in aid of the civil power’. New Zealand possibly provided defoliants for the Vietnam war.