By early 1942 the war in the Pacific was going badly for the Allies. Singapore fell in February; Darwin was bombed days later. Townsville, the largest city in Australia's north, suddenly found itself a frontline port and the principal staging base for the looming fight over New Guinea. Its airfield at Garbutt was the prize, and the prize needed guarding. Two batteries of the 16th Heavy Anti-Aircraft unit were positioned to cover it. One, at Rowes Bay, became X Station. The other rose here, on Mount St John, directly west of the main runway and roughly two and a half kilometres away. When it was finished at the end of April, this was Townsville's largest and most modern battery: four gun positions, four buried magazines, and a semi-underground command post where plotters tracked the height and bearing of every aircraft in the sky.

The gunners called it Y Station, and their work was as much vigilance as violence. Every aircraft approaching Garbutt was assigned a correct lane of entry. Anything that strayed from it was to be treated as hostile and fired upon. The post was wired by telephone to the fighter sector headquarters and manned twenty-four hours a day, which meant long stretches of nothing punctuated by sudden alarm. On 21 March 1942 the first Japanese aircraft seen over Townsville was spotted high over the city, silvery against the noon sky, almost certainly a long-range Mitsubishi reconnaissance plane sent to photograph the airfields. The men below could not yet fire accurately; their open gunsights had not been fitted. They could only watch it cross the sky and disappear, knowing exactly what it meant. Someone, somewhere, was planning a raid.

It came in late July. On three nights, huge four-engined Kawanishi flying boats, the type the Allies code-named Emily, lumbered down from their base at Rabaul to attack Townsville. The first raid, on the night of 25 to 26 July, dropped its bombs harmlessly into the sea off the wharves. Y Station held its fire. But early on 28 July, searchlights at Rowes Bay caught a lone Emily at ten thousand feet, and the Mount St John guns opened up. After twenty rounds a shell burst close to the aircraft's nose, and the rattled crew jettisoned its bombs over the empty ranges south of the city. The hill had done its job. A final raid on 29 July scattered bombs into Cleveland Bay and a paddock at Oonoonba before American fighters drove the intruder off. No one in Townsville was killed in any of the three raids, a fact owed in part to the gunners who made the night sky dangerous.

The 16th Battery disbanded in 1944, and after the war the hill was sold, quarried, and half-forgotten. Industry crept up its flanks; a sewage treatment plant sits nearby now. Yet the bones of Y Station survive better than almost any other wartime gun position in Queensland. Two of the magazines stand fully exposed, their stairs torn out and lying where the quarrymen dropped them. The other two remain buried, holding whatever the gunners left behind. The command post is structurally intact, its single steel door still hanging. Heritage-listed in 1999, Mount St John is the only Townsville battery known to have actually fired on the enemy, both before and after the Battle of the Coral Sea turned the tide. Stand among the platforms and the sight lines to the old airfield are still clear. That clear view was the whole point.