Imagine a concrete lined room, hazy with cigarette smoke and lit only by a few shaded lamps which hang from the ceiling. In the centre, women in uniform surround a large table, atop of which a map of the Canterbury region is spread. Occasionally one of the women might adjust her headset and then, using a stick similar those wielded by croupiers at gambling tables, move a marker into a new position on the map. From a gallery above, officers look down in silent concentration. A runner enters the room and wordlessly passes a note to one of the officers. Then, from over the radio, a frantic voice breaks the tense atmosphere.
“Godley Battery has fallen. Japanese troops have taken Lyttelton.”
Defence of the South Island
For many nights the residents of the hillside suburb of Cashmere had been woken by the sound of blasting accompanied by ground tremors. The war was in its third year and New Zealand was under the threat of an invasion from the Empire of Japan. Throughout most of 1942 black out practices had become a common occurrence in Christchurch. Those living on the hill simply assumed that the military was conducting yet another clandestine operation.
The New Zealand military already had a presence in Cashmere. In July of that year the Government had commandeered Cashmere House, the property of John Frederick Cracroft Wilson, to act as Combined Headquarters Southern Command.
Built in 1909 to designs by Samuel Hurst Seager, Cashmere House was set in a depression atop the Cashmere Hills. Reached via a long driveway which wound its way up the hill, the house overlooked an expanse of trees, lawns and gardens. Within, the house contained more than thirty rooms, enough to accommodate the different departments of the Air Force, Navy and Army that were required to oversee the defence of the South Island. Yet while it provided adequate office space, a civilian house was not designed to withstand the threat of aerial bombardment, nor was a house of that size likely to remain unnoticed by any invading troops.
In preparation for its war with Germany, Britain had established subterranean control stations so that the nation’s defence could be coordinated during aerial bombardments by the Luftwaffe. Anticipating the Japanese invasion, Southern Command adopted the same approach. No sooner had the military taken over Cashmere House than it started the construction of what was intended to be a secret, underground command bunker.
To the northeast of the house two separate adits (passage tunnels) were dug into the hillside. Throughout the excavation, the soil and rock was taken via a purpose built rail and disposed of in a nearby valley. Initially proceeding southward, the adits then curved westward, so as to offer protection against external explosions. From there the adits opened into a large U shaped chamber which had been excavated from the bedrock.
Pre-stressed concrete ribs, constructed at a Public Works Department factory at the Birches near McLean’s Island, were used to brace the chamber. To set them in place a specially designed machine was manufactured at a workshop in Temuka. It was not necessary to set all the ribs in place, only those that were needed to stabilise the caverns. As a result most of the walls remained natural rock
A communications tunnel, intended only for the use of officers, was built to connect the chambers to Cashmere House. The tunnel was accessed from the basement in the house and descended on a slight gradient to the chambers. A ventilation shaft set at the midway point in the tunnel provided fresh air to the chambers.
Initial plans drawn up by the Public Works Department show the extent of the military’s aspirations. The plans show that the northern wing of the chamber was to house an office and separate rooms for the Army, Navy, and Air Force, along with a telephone exchange and cypher room. The southern chamber wing was to house another cypher room and a room for teleprinters. The two wings were connected by a western chamber and a further corridor.
The western chamber was intended to consist of two levels. The northern end would be the combined operations room. The southern end was the plotting room. Ladders would provide access to the upper floor. There, a gallery would allow observers to watch the movement of air force units being co-ordinated on the plotting table. It was proposed that the bunker would also contain kitchens, bedrooms and toilet facilities.
Work on the chambers continued until April 1943 when the war in the Pacific turned against the Japanese and the threat of an invasion was no longer considered a possibility.
Fire and concealment
By the end of 1944 the Army and Navy services had already vacated Cashmere House, leaving only the Air Force to occupy it. In November, plans were arranged for the Air Force to hand the building and its grounds back to the trustees of the Sir J.C. Wilson estate by the start of December. Yet before this could take place, on 12 November 1944 at 11:40pm, the building caught on fire. Although the fire was eventually brought under control, by 2am much of the building had been lost. The cause of the fire was never discovered.
By January 1945 details of the caverns had been leaked to The Press. The resulting article was accompanied by photographs which showed not only the district engineer of the Public Works Department inspecting the interior of the chambers but also the machines used to construct them. As it was still wartime, the defence force refused to discuss the existence of the caverns and no further information was made public. The tunnels were sealed and the owner of the property bulldozed the entrances to discourage any members of the public from attempting to enter them.
Following the conclusion of the war in September 1945 the existence of the caverns soon faded from public memory. Sworn to secrecy, those who had assisted with the construction or who had served as guards at the Cashmere property never spoke openly about what lay hidden beneath the grounds of the former house. As generations passed, even incoming members of the military seem to have remained unaware that such a project had ever been undertaken.
A chance discovery
The caverns may have remained hidden from the public for longer were it not for the retirement of a nurse at Princess Margaret Hospital. In 1987, while attending a farewell function being held for his mother, TVNZ reporter Jeff Field was told of the caverns by the hospital gardener.
Intrigued, he visited the Ministry of Defence library where he found the aforementioned Press article. Since he was due to take up a new role, Jeff assigned the investigation to another reporter, Bill Cockram. Following the 1944 fire, a new house had been erected on the site of Cashmere House. Upon visiting the owner, Bill Cockram learned that the building was experiencing problems with drainage. As such, the owner was interested to discover what lay beneath his house and gave Bill permission to proceed with his investigation.
Given that the former grounds of Cashmere House had been redeveloped, the only sign that anything lay hidden beneath was the protruding end of a pipe which marked the location of the ventilation shaft. After breaking the seal with a jackhammer, Bill next contacted Tim Williams of the Canterbury Caving Group. Together, with fellow caver, Bud Chapman, a television crew, and the property owner, they abseiled down the ventilation shaft and entered the caverns.
It was the first time that anyone had done so since they were sealed.
The television crew filmed the experience and the resulting documentary was screened as part of The Mainland Touch. Bill Cockram’s discovery, coupled with the release of the documentary, led to renewed public interest in the caverns. In December 1987 the Heathcote County Council’s planning committee even considered listing the bunker as a historic place.
The university moves in
The University of Canterbury, however, already had a vision for the caverns. Initially their ring laser laboratory which measured variations in the earth’s rotation was set on the top floor of a building on the Ilam campus. Yet such a location meant that the experiments were constantly being disturbed by wind, heat, and the movement of people. After considering the military tunnels in Lyttelton and a seismological station at Gebbies Pass, it was eventually proposed to make use of the caverns.
So it was, for the first time since they were excavated from the earth, the caverns came to be formally occupied. Yet rather than being used to co-ordinate a desperate defence against an enemy invasion, the caverns became a temporary home for numerous PhD students and international scientists who joined together to perform research that might benefit humanity.
In 1995 the Christchurch City Council took ownership of the caverns and in the following year the university installed the CII ring laser. The university continued to use the caverns as their laboratory, installing new equipment, and producing new results. Open days were also held for those members of the public who were curious.
Although they were built to withstand the impact of an enemy bombardment, the facility was rendered unsafe by the Canterbury Earthquakes. They have remained closed to the public ever since.
Find out more
- See more photos of the Cashmere caverns in Kete Christchurch
- See Ministry of Defence plans and drawings for the caverns from Archives New Zealand
- Read more about the history of the University of Canterbury’s ring laser experiment.
- Find material about the Cracroft Caverns in our catalogue.