SUBTERRANEAN CHAMBERS

Press, Volume LXXXI, Issue 24471, 22 January 1945, Page 8

SUBTERRANEAN CHAMBERS

Use For Combined Headquarters

EXCAVATIONS AT CASHMERE

Intended for use in a national emergency as a combined headquarters for all branches of the armed forces, plans were completed in 1942 for the construction of a series of. underground chambers on the Cracroft Wilson Estate at Cashmere. Japan nad just entered the war, and with the possibility of an invasion of the Dominion, the work of constructing the underground headquarters was pushed ahead as rapidly as conditions permitted. Fortunately, it became apparent that the headquarters would probably not be required, and work on their construction was abandoned before they had been fitted up. although all the excavations and such reinforcing work as was necessary in the interests of safety were completed. The secret of the intended use of the excavations at Cashmere was well kept, and few, if any, of the residents of the surrounding suburbs who heard the blasting of the rock by the workmen knew what they were constructing. Details of the construction and lay-out of the underground chambers have now ■ been released to “The Press.” The Cracroft Wilson property at Cashmere was taken oiVer by the Government on the entry of Japan into the war, and the big homestead was at first used as a combined headquarters for the forces. Later it was taken over by the Air Force as its Southern Group headquarters. Arrangements were made last- year for the Air Force authorities to hand the property back to its owners, the trustees of the Sir J. C. Wilson Estate, in the first week of December. On November 12, 1944, the homestead on the estate was destroyed by fire. Dimensions of Station Soon after the property was taken over by the Government, instructions were given for the building of underground headquarters oh similar lines to those of underground control stations established in various parts of England, for the control of defence activities under aerial bombardment. The Public Works Department wag entrusted with the task of driving tunnels into the hill below the CracroftWilson homestead, and with the excavation of a combined headquarters to specified requirements. The underground station excavated consisted o| one main back chamber, 76 feet long, *25 feet wide, and 18 feet 6 inches high ‘when completed. The measurements are thipse of internal dimensions. In addition to the main chamber there were two adjoining chambers, connected by adits (underground passage-ways), and built in the form of a hollow square. These chambers were 107 feet'long overall, 20 feet wide; and 17 feet high, except for one section adjoining the mamback chamber, which was 25 feet wide and 18 feet 6 inches high. The ceilings of the whole of the station were from 50 feet to 80 feet underground, the; cover being,of good quality volcanic tuff and scoria, superimposed by loess. There was at least 20 feet of rock above the underground chambers. Access to the station was given by two construction adits, approximately nine feet high and seven feet built on a very slight grade, and curved like a hockey stick to give protection against blast. Each of these adits was about 200 feet long. In addition, the underground station was connected to the cellar of the Cracroft Wilson homestead by an access adit on a grade of one in five. This passageway was about 400 feet long, with steps from the cellar of the house and into the combined operations station. The adit from the house was pierced by an air shaft, leading to the ground level 55 feet above, and-supplying air to all parts of the underground station. As the urgency of the Dominion s situation in the war appeared to demand rapid completion of the tions station, and as the number of tunnellers who could be employed on the job was limited, everything was done to expedite the work of excavation. At the same time, the tunnel roof lining was manufactured in precast reinforced sections at the Public Works Department’s concrete factory at the Birches, where facilities existed for' the work. The object of this was to ensure the rapid completion of the tunnels, as the members-of the root linings could be put in place without ' damage as the excavations proceeded The roof members were constructed as reinforced arch ribs for the 25 feet fnd 20 feet width roofs Each nb was about-two feet wide and one foot thick, interlocking, .and with provision for water collection. The weight of eacn was about three and a half tons. Special Machinery Developed mvie. niacins of the pre-cast ribs in demanded the design and manufacture of suitable elevating gear Thiswas designed by engineers of he ' Public Works Department, and built at the Temuka workshops. It consisted of a truck constructed from an Athv waggon, with a hydraulic ram borrowed from the shield equipmen at the Tekapo tunnel. The pre-casi xib was placed on the waggon outside the tunnel, and then on the tunnel tramway, which had been -carefully centred. The fitting ram was then used to elevate the rib, into the air, and swing it into posi tion on top of the orainary cormrete walls at the sides of the tunnel. Three lifts were required for the placing of each rib. A crew of four men manned the machine, and up to seven ribs wee placed for each eight hours worked. This method iof lining tunnels had never previously been employed in th When'the n japanese threat to New Zealand receded, the necessity for expeditiously completing the tunnels disappeared. but the excavation work was already well advanced. Only such concrete ribs as were necessary for safety were actually placed m position Where a good scoria roof existed, the tunnels were left in the .bare rock. The whole of the back chamber was roofed however, and American-type timbering in one of the other chambers was also allowed to remain. Except for the stairways, some work near the cellar o the house and for a safe distance along the passage-way from it, and for a short distance from the entrances until solid ground, was reached, the adits were left unlined; . All the excavations were in very dry ground. Excellent ventilation for the chambers and their approaches was obtained through the air vent in the passage from the house. Elaborate Arrangements Planned Had the full plans been carried out, and the fitting-up of the station completed. a fully self-contained headquarters would have been created, with independent lighting and air conditioning system, wireless apparatus, telephone and telegraph facilities, and all the paraphanalia associated with the stations built to withstand the blitz in Great Britain. In the main chamber, which would have been under the control of the Air Force, was to stand a big plotting table, on which the movements of aircraft could be traced. Overlooking this were to be galleries running round the walls, from which observers could look on. In an adjoining room, reports of the movements of the armed forces would be received. Another room was to be the actual combined operations headquarters, while connected to the main room by passages were to be rooms for the (commanding officers, the Army, Navy and Air Force officers employed at the station, technicians, and other personnel. The original plans envisaged the construction of part of the station in two storeys. Various sections of the station were separated by blocks of solid rock, and were connected oy passages running through it. To-day, the excavations remain as an enduring symbol of the menace once imminent to New Zealand; and their unfinished state serves as a reminder of the horrors which the Dominion was spared.