During the Second World War, New Zealand utilised approximately one hundred and thirty British Ordnance QF 3.7-inch Mk 3 Anti-Aircraft guns.[1]
Deployed across New Zealand at fixed and mobile sites with wartime scales of ammunition totalling 428,032 rounds, these guns stood ready during the war years in anticipation of Japanese air raids. New Zealand’s anti-aircraft defences were never tested, and with the immediate threat removed, the guns were placed into storage, and the ammunition was returned to depots for refurbishment. However, due to the considerable amount of ammunition returned to New Zealand’s depots at the war’s end, storage capacity was soon outstripped, necessitating the storage of large quantities under tarpaulins in field conditions.
By 1954, 17,000 rounds of 3.7-inch anti-aircraft ammunition had been stored in unsuitable conditions at the Liverpool Range outside Trentham Camp. With sufficient 3.7-inch stocks available to meet training needs in other depots, the Liverpool Range stocks were considered surplus. Although initially intended for inspection and refurbishment at the Kuku Valley Ammunition Repair Depot, inspections revealed that the Liverpool Range stocks had deteriorated to the point where destruction was the only option.
A plan was formulated to transport the 17,000 rounds of unstable 3.7-inch ammunition from its storage area at the Liverpool Range across the valley, approximately 1.4 kilometres, to the demolition area at Seddon Range. The explosive content was destroyed there, and recoverable components, such as the brass casings, were collected and sold as scrap.
The Royal New Zealand Engineers constructed a road between the Liverpool and Seddon ranges to create a safe working area around the stacks and provide access to them.
Due to the detonation risk of the ammunition and its storage containers and the likelihood of an explosion, a modified armoured truck and trailer were constructed to facilitate the transportation.
The 3.7-inch round was a 12.7kg single piece of ammunition consisting of a cast steel projectile with a tapered nose filled with Amatol, TNT, or RDX/TNT explosives, mounted in a brass casing. The brass casing contained an explosive primer and a cordite propellant charge that could propel the projectile to a maximum ceiling of 9,000 meters or a horizontal range of 15,000 meters. Each 3.7-inch round was packed in a fibre cylinder, with two rounds packed into a C235 steel case.[2]
With 17,000 rounds in 8,500 cases, ten cases (twenty rounds) were transported from the Liverpool Range to the demolition area at a time. The cases were then unloaded at the demolition range, and in batches of four, the rounds were detonated.
From June 1955, five or six detonations occurred daily, with the frequency and strength of the explosions causing some distress to residents, with the Upper Hutt Council questioning the Army on the reasons for the explosions.[3] Another resident forwarded a strongly worded protest letter to the editor of the Upper Hutt Leader Newspaper.[4]
Letters to the Editor
Dear Sir, The terrific explosions at the Trentham Camp which have wrecked our nerves for some considerable time, are the subject of this letter. Mr Editor. The world is at peace, yet we are at war (by the sound of things) in this beautiful valley in which we live. Every day these loud blasts shake our houses, waken our babies end sleeping little ones also elderly people having an afternoon nap, have a rude awakening, It takes very little imagination to realise the effect this bombing has on the nerves of bed-ridden patients at the Silverstream hospital. I ask you to publish this letter in the hope that the authorities will cease-fire, or at least explain why and how long this blasting is to be endured.
I am etc.,
ATOMIC BOMB
However, the explosive destruction of the old ammunition continued, and the daily explosions became an accepted and routine feature of life in Upper Hutt.[5]
The demolition of the 17000 rounds of unsafe 3.7inch ammunition was concluded in December 1957. The destruction had proceeded without incident, with the local residents thanked for their considerable forbearance in putting up with the noise of explosions nearly every day.
Notes
[1] Damien Fenton, A False Sense of Security: The Force Structure of the New Zealand Army 1946-1978, Occasional Paper / Centre for Strategic Studies: New Zealand: No. 1 (Centre for Strategic Studies: New Zealand, Victoria University of Wellington, 1998), Bibliographies, Non-fiction.
[2] Great Britain. War Office, Anti-Aircraft Ammunition: User Handbook (War Office, 1949).
[3] “The “Boom” from Trentham Camp,” Upper Hutt Leader, Volume XII, Number 28, , 28 July 1955.
[4] “Letters to the Editor,” Upper Hutt Leader, Volume XII, Number 29, , 4 August 1955.
[5] Howard Weddell, Trentham Camp and Upper Hutt’s Untold Military History (Howard Weddell, 2018), Bibliographies, Non-fiction, 187-88.
