Of all the Ammunition magazine areas constructed in New Zealand during the Second World War, the Belmont magazine area nestled in the hills north of Wellington between the Hutt and Porirua was the largest and closest to a large population area. In the early 1970s, following the removal, disassembly for scrap, and destruction of its stocks, Belmont’s life as a magazine area concluded with the land reverting to civilian use. As with any retired military facility kept out of the public eye during its operational life, urban legends and rumours thrive about secret tunnels and forgotten caches of buried military material. In this respect, Belmont is no different as items such as empty 3.7-inch Anti-Aircraft projectiles are occasionally discovered, fuelling such rumours. Although there is little evidence to support the stories and urban legends, Belmont does have some secrets from its wartime past. The most significant is that Belmont was the home to the bulk of New Zealand’s chemical weapon stockpile.
As the threat of war with Japan became inevitable in 1940, the New Zealand Government initiated a full mobilisation of New Zealand’s home defence forces. By early 1942 this mobilisation saw two Infantry Brigades deployed to Fiji and Three Divisions and several independent Brigades mobilised for home defence.
This massive mobilisation initiated a rearmament program resulting in vast amounts of war material from the United Kingdom, Canada and the United States being delivered to New Zealand. Included as part of the infusion of new weapons and equipment were the required scales of ammunition required for each type of weapon system. Ammunition scales used by New Zealand were based upon the standard British scales. They included all the ammunition natures needed by New Zealand for use in the Pacific and home defence, including Anti-Tank, High-Explosive, Smoke and a stockpile of Chemical rounds consisting of,
- 112,770 25-Pounder Chemical rounds, and
- 10,300 4.2-inch B4 (Tear) and Y4(Blister) chemical mortar bombs.
With consignments of ammunition due to arrive in New Zealand in late 1942, construction of the new ammunition magazine areas had been initiated in 1940, with the construction of the Belmont Magazine Area beginning in September 1942. The Belmont Magazine Area consisted of sixty-two Magazine buildings, with buildings 28 and 29 dedicated to holding chemical rounds from late 1943.
All the 4.2inch Bombs were stored at Belmont with the recommended distribution of the 25-Pounder chemical rounds,
- 30,000 rounds to the Northern Military District
- 30,000 rounds to the Southern Military District
- 52,770 rounds to the Central Military District Belmont Depot
However, records are uncertain if this distribution occurred, so it is quite probable that the entire stock of 25-Pounder ammunition was held at Belmont.
The New Zealand Stockpile was significant as a lethal percutaneous dose of mustard was 4.5 gm. With 300 tons of the agent in the NZ stockpile, the potential lethal doses held in Belmont were approximately 60 million. To put the size of the stockpile in context, it was equal to 5% of the United States Stockpile in 1993.
The use of Chemical Weapons was highly controlled and only to be used in retaliation if the enemy used it first. Although US forces on Guadalcanal had captured some Japanese Chemical Weapons, the NZ Deputy Chiefs of Staff were confident that there did ‘not appear to be any other or greater evidence that the Japanese propose to use gas in this area’. However, it is believed that 3 NZ Div did deploy with Chemical rounds for their 25-pounders just in case.
If Chemical rounds were deployed with the 3 NZ Div, they were returned to New Zealand in 1944 and stored at the Kelms Road Depot at Ngaruawahia alongside the other natures of ammunition utilised by the Division.
Following the war, the disposal of wartime ammunition became a standing task for the RNZAOC Ammunition functions as damaged, obsolete, and surplus stocks were disposed of by a variety of methods.
Ammunition that was damaged was often disposed of by demolition; for example, the destruction of 3.7-inch Anti-Aircraft ammunition issued to units and returned to Depots took up to 1957 to complete.
The stockpile of chemical munitions was dumped at sea, with two dumping operations found in archival sources.
- Two hundred tons of chemical shells scuttled on the tug Maui Pomare at the 100-fathom line in the Hauraki Gulf in April 1946.
- One thousand five hundred tons of 25-Pounder chemical shells and twenty tons of bombs had been dumped by the Marine Department steamer Matai off the Wellington coast by October 1946.
Stock from the Belmont magazine area was delivered by Army personnel to the wharf at the RNZAF base at Shelly Bay in lots of 250 Tons and loaded onto the Marine Department steamer Matai. All possible safety precautions were applied with each crew member was issued protective capes, respirators and gloves. With special chutes constructed, cases of shells were jettisoned fifty Nautical miles off the Wellington coast in the Cook Strait Canyon, which reaches depths of three kilometres.
The dumping of the Chemical munitions was well publicised, with newspaper articles describing the disposal operation;
Stored since 1943, 1500 tons of gas shells are to be dumped at sea by the Matai. Fuses have been removed from the 25lb shells that contain the gas, but to ensure that there is no risk to those carrying out the work, full Admiralty and War Office safeguards will, be taken. The gas is of the blister variety. The boxes containing the shells will be filled with sand to guard against possible leakages. Each box is painted with a substance that will indicate even a pinpoint of escaped gas.Northern Advocate, 18 September 1946
Although the archival records that at least 15,220 tons of Chemical munitions had been dumped at sea by the end of 1946, there is no accurate reconciliation of the actual number of rounds disposed of. However, it is a reasonable assumption that New Zealand had no desire to maintain a contingency stock of Chemical weapons and that all wartime stocks were disposed of by the end of 1946.
 F Grattan, Official War History of the Public Works Department (PWD, 1948).
 “Defence Works – Magazine – Belmont Hills,” Archives New Zealand Item No R22435088 (1942).
 “H-19 Military Forces of New Zealand Annual Report of the General Officer Commanding, for period 1 April 1957 to 31 March 1958,” Appendix to the Journals of the House of Representatives (3 July 1958 1958).
 “Ammunition – Disposal of unserviceable ammunition 1945-1952,” Archives New Zealand Item No R21465842 (1945).
 A Hubbard, “Chemical War: Our seabed legacy,” New Zeland Listener, 16 January 1993.
 “Gas Shells to be Dumped at Sea,” Northern Advocate, 18 September 1946, https://paperspast.natlib.govt.nz/newspapers/NA19460918.2.17.