During the Second World War, New Zealand had utilised approximately one hundred and thirty British Ordnance QF Mk 3 3.7inch Mark 3 Anti-Aircraft guns.[1]

Deployed across New Zealand at fixed and mobile sites with wartime scales of ammunition, these guns sat ready during the wartime 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 with the ammunition returned to ammunition depots for refurbishment. However, due to the considerable amount of ammunition returned to New Zealand’s Ammunition depots at the war’s end, the capacity to hold all of the returned stock soon be outstripped with large amounts required to be stored under tarpaulins in field conditions.

By 1954, 17000 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 to be inspected and refurbished at the Kuku Valley Ammunition Repair Depot, inspections revealed that the Liverpool Range stocks had deteriorated to the state where destruction was the only option.

A plan was formulated to transport the 17000 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, where the explosive content was destroyed, and recoverable components such as the brass casings recovered and sold as scrap.

To create a safe working area around the stacks and provide access between the Liverpool and Seddon ranges, the Royal New Zealand Engineers undertook the engineering task of creating access to the stacks and constructing a road between the ranges.

Due to the detonation of the ammunition and its storage containers and the likelihood of an explosion, a modified armoured truck and trailer was 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 case consisted of an explosive primer and a cordite propellant charge that could propel the projectile to a maximum ceiling of 9000 meters or a horizontal range of 15000 meters. Each 3.7-inch round was packed in a fibre cylinder, with two rounds packed into a C235 steel case.[2]

With 17000 rounds in 8500 cases, ten cases (twenty rounds) were transported from the Liverpool range to the Demolition area at a time. The cases were the 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 local 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 with the daily explosions becoming 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.

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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.