Ryan took his idea to Vic Mann, the mine superintendent, who offered the company's equipment and the services of underground foreman Wally Onton to run the job. The miners volunteered their own off-duty hours. Working through March and April 1942, they drove three parallel tunnels, or adits, straight into the hillside, then joined them at the back with a crosscut to form an E-shaped warren of roughly 100 meters of passage. The drilling, blasting, and mucking out, the brute labor of moving broken rock, took only about two weeks. A vertical shaft to the surface provided ventilation and an emergency ladder. These were men who carved tunnels for a living, and they turned that hard-won skill to the task of protecting their own town.

What they fitted out was no mere bomb shelter. Timbered like a mine with Oregon and native hardwood, lined in places with gidyea logs, the tunnels held male, female, and maternity and children's wards, a surgical theater, and a delivery room. Electric lights burned underground, a telephone connected it to the world above, and buckets of water and sand, stirrup pumps, and shovels stood ready against fire. Dr Ryan kept it stocked at all times with linen, dressings, medical equipment, and pharmaceuticals. Once a week the staff ran a drill, nurses and orderlies wheeling the less-seriously-ill patients up the steep gravel path and into the cool dark of the hill. It was a fully working hospital that waited, ready, for a catastrophe everyone expected.

The bombs never fell on Mount Isa. It became clear that the raids on Darwin and the northern towns were harassment rather than the opening move of an invasion, and after the battles of the Coral Sea and Midway shattered Japanese naval power, the threat receded entirely. The drills stopped. The underground hospital, built for emergency, settled into quieter uses: a cool dormitory where nurses slept on the hottest nights, then, as such places do, a store room slowly filling with files and discarded equipment. After the war, with security grown lax, children slipped in to play among the abandoned medical supplies and pharmaceutical bottles still scattered on the earthen floor.

The hill nearly swallowed the place for good. In the 1960s its entrances were buried under rubble from a new hospital wing, and for a decade it lay sealed and forgotten until the fill began collapsing, in 1977, again in 1988 and 1992. Each reopening reignited debate, sharpened by Australia's renewed interest in its wartime sites. Then fire struck twice, in 1994 and again in 1997, the old files and X-ray plates feeding the flames while firefighters, unable to fight water against it, finally smothered the tunnels with high-expansion foam. But the community had decided the hospital was worth saving. Restored from old photographs between 1997 and 2001 and now reached through the Beth Anderson Museum, the only entirely underground hospital known in Australia stands again, a monument to the fear of 1942 and to the miners who answered it with their hands.