Access

Ferries operate to Waiheke Island from Auckland’s Ferry Terminal and Devonport. On arrival at Oneroa, hire a car or arrange taxi transport. In Onetangi, turn into Waiheke Road and follow the signposts to Stony Batter. There is no public transport to Stony Batter.

The tunnel complex is a 15-minute walk from the locked gate. The tunnels are currently closed.

Track

Follow the metalled access road for 20 minutes to the signposted tunnel entrance.

Geology

The farmed area is mottled with an arrangement of andesitic boulders, creating a curious landscape, interspersed with grazing sheep. The boulders, which give rise to Stony Batter’s name, were also used as aggregate for the vast quantities of concrete needed to construct the huge complex of underground fortifications.

European History

Above ground the remains of the World War 2 guns are strikingly evident and easily explored by wandering through the paddocks between the gun pits, ventilation shafts and derelict buildings. However for the best appreciation of the immensity of the gun emplacement infrastructure, take a walk through the vast underground network. A torch is essential.

Had you been an Auckland resident just before World War 2, the problems of city living would not have revolved around traffic, pollution and crime. The greatest threat to your security would have been the possibility of a German cruiser sneaking into the Waitemata Harbour and lobbing shells over Motutapu, with the potential to destroy the city’s infrastructure.

During the 1930s, the Government searched for possible gun battery and fort sites. They realised if they constructed guns with a sufficiently long range at Stony Batter on Waiheke Island, they could block off Cape Colville to Kawau Island. With a twin set at Army Bay on the Whangaparoa Peninsula, they could protect the northern entrance to the Gulf and provide a safe for anchorage for Allied ships in Auckland waters.

They designed tunnel systems unique to the contours of the land and employed 189 men to dig the vast subterranean complex. A wharf was built at Man O’ War Bay and connected to the site by a road, which carried vehicles bearing heavy machinery, sand and cement.

The biggest problem during construction was the whole operation had to be kept secret - not an easy task when the gun barrels alone weighed 28 tonnes and were 12-metres-long. The nearest power pole was (and still is) 5.5 km away, necessitating the use of generators to provide electricity.

The construction of 1 km of tunnels (each surrounded by 30 cm of concrete), 3 gun emplacements with associated underground magazines and explosives stores, control rooms, living quarters, engine rooms and a pump house was a logistical nightmare. The complex was supposed to be built in the 1930s but was put off because of the Depression. It was started in the early 1940s and finished in 1945/46, after the end of the war.

A partially restored bunkroom, used by staff who manned the guns, now serves as an exhibition room and display centre at the tunnel entrance. This is in the process of being painstakingly and comprehensively restored by the Stony Batter Protection and Restoration Society Incorporated.

They were formed in 1999 to preserve and restore, as far as could be done, the artefacts. This team of ‘dedicated nutters’ have spent 18 months cleaning the tunnels and gun pits. When they first rediscovered the site after decades of neglect under Government ‘protection’, the bottom tunnel was flooded calf deep and lay strewn with animal bones, sheep carcasses, glass, concrete, bricks, and tree trunks.

At the entrance to the tunnels is the dead end blast chamber, which has 1-metre-thick concrete at the end wall. The tunnel turns left then right before continuing in the same direction. The idea behind the system allowed a blast to be absorbed by the dead end, preventing it’s penetration through the tunnel system.

The first room is the magazine, which is approximately 24m-long, 8m-wide and 4m-high. It held 370 shells in 3 pyramidal stacks, separated with wooden guides like a wine rack. A steel rail around the top dangled a block and tackle, which moved shells around the magazine. The shells, each weighing 172.5 kg, were hoisted up a shaft to the gun pit.

The explosive charge was detonated by cordite, which was stored in a separate room. The crew manning the store had to change out of their uniform and put on cotton clothes to avoid static electricity build up and the possibility of explosion.

Off the bottom tunnel is the engine room, which housed two Ruston Hornsby diesel engines. These were the heart of the entire operation as they provided power to the guns, motors for the pumps and the light in the tunnels.

After the pump room is a ladder to the gun pits. The gun barrels were approximately 12-metres-long and nearly 1-metre-wide at the breach. The guns were the fifth biggest in the Commonwealth after examples in England, Canada, South Africa and Gibraltar.

The guns were proofed to work out plotting tables. By altering the angle of elevation, different distances were attained. There is no consensus on how many times they were fired, but they were never used in wartime. In the 1950s a gun was fired, but the percussion from the blast broke windows in Coromandel Town, nearly 30 kms away.

The shells were loaded with 2 bags of cordite explosive, each weighing 27.5 kg. The gun operators would shut the breach and fit the fuse, which was electrically fired. The obdurator sealed the barrel and stopped the backflash as the guns fired. For the following 14-16 seconds after firing, water and compressed air blasted through the barrel to cool down and blow out the gasses through the muzzle. Turnaround between firing was normally 30 seconds, including changing the elevation. The guns had a range of 32 km.

Exiting the gun pit, Kawau Island is a mere speck on the horizon. In the far distance would have been the guns at Whangaparoa, catching enemy ships in a crossfire.

The fort was shut at the end of 1957 when the coastal defence regiment was mothballed. In the 1960s the guns were chopped up and sold for scrap, with the plate steel being sold to Japan. The tunnels were left sealed but unprotected.