Southern Group HQ
Cracroft Cavern general layout
In response to the Japanese threat to New Zealand's security in early 1942, the War Cabinet authorised the provision of operational shelters in the four main centres to enable Combined Headquarters (Army, Navy and Air) to carry on in the event of attack. The Dunedin proposal was dropped, while the Wellington and Christchurch projects were discontinued when the war situation improved.
In the early months of 1942 the Cracroft-Wilson homestead on Cashmere Hills was taken over and adapted for use as a combined headquarters and a series of large chambers excavated underground to provide protection for headquarters staff for extended periods. Work was carried out by the Public Works Department under conditions of strict secrecy. Construction stopped in 1944 and the Cracroft-Wilson homestead was destroyed by fire while the military were vacating the site. The entrances to the underground complex were later sealed. The existence of the caverns became the stuff of urban legend in Christchurch until excavations were carried out in 1987. The caverns later became the site of a ring laser experiment set up by the University of Canterbury's physics department to measure "subtle perturbations in the Earth's rotation".
While these plans are held in the Christchurch Office of Archives New Zealand, any relevant files created by the Public Works Department in Christchurch were presumably removed to Wellington during the War. The Head Office file reference is PWD 23/687/2. The Christchurch plans were hidden under the innocuous subject title: 'Underground Tank'.