The impressive remains of a Second World War 9.2 inch Counter Bombardment (CB) Heavy Coast Defence Battery survive at Stony Batter, with three concrete gun emplacements and an extensive system of underground chambers connected by stairs and tunnels.
The guns and equipment have been scrapped, but the remaining structures are much as they were when abandoned by the army after the war.
Note: The tunnels at the Stony Batter Historic Reserve are currently closed to the public.
Counter bombardment batteries
The counter bombardment battery system was developed in the 1930s to take advantage of the longer-range capabilities of the larger 6 and 9.2 inch guns. To enable the guns to hit their targets beyond the line of sight a series of observation posts had to be established forward of the gun positions. These relayed back information which was converted into ranges and bearings for the guns. It required a far greater degree of sophistication in terms of range-finding, communication and calculation than had been used before in a New Zealand battery.
The Waiheke battery was part of a larger coastal defence system protecting Auckland Harbour and its approaches from enemy ships. Two other counter bombardment batteries were located at Whangaparaoa (9.2 inch) and Motutapu Island (6 inch), and a network of observation posts were established at Rangitoto Island (the command post), Tiritiri Matangi Island and other locations.
There were also close defence batteries at Castor Bay, Whangaparaoa and Rangitoto, examination batteries at North Head and Fort Takapuna, and minor works at other points around the harbour. An anti submarine boom protected the inner harbour and minefields and detection devices were laid to protect the harbour approaches.
The guns used at Waiheke could fire a shell out to 31,300 yards (over 30km) with a possible rate of fire of one round per minute.
They were mounted within their emplacements on revolving platforms that could rotate 360° and elevate to 35°. Around the floor of each emplacement were lockers for ready use ammunition and a hoist to a magazine below, where the shells and cartridges were stored. A passage led off to a pump chamber containing electric motors and pumps which connected to and operated the gun, and a stairway led down to the underground chambers. Near the stairs was an artillery store containing the equipment and fittings for each gun.
The engine rooms contained a workshop, three diesel engines and generators which provided the power to light the tunnels and operate the equipment, including the guns. There was a fuel store near the engine room. Plotting rooms contained the equipment used to calculate the ranges and bearings for the guns, and at each of the tunnel entrances was a concrete building called a War Shelter, where the men manning the battery would wait to be called to action.
9.2 inch CB batteries were approved for Auckland's defence in 1939, but construction was delayed for reasons of cost until the activities of German raiders in New Zealand waters in 1940-41 and the entry of Japan into the war in late 1941 made them a high priority. The Waiheke site was chosen in 1942 and the Public Works Department began construction in early 1943.
The tunnels and underground chambers were dug by hand, moulds for the walls and ceilings constructed and concrete pumped into them. Aggregate was obtained locally from the prominent rocky outcrops that give Stony Batter its name.
The design for the tunnels and chambers was adapted from plans for the Tawa Flat Railway Tunnel project. The task of building the defences was made more difficult by their isolated position. A road from Man O War bay had to be built and a work camp set up before work could start, most materials had to be barged to the island from Auckland, and the workforce was smaller than planned.
The work was eventually completed, behind schedule, in 1944 and the costs ballooned from the projected £140,000 to £327,966, excluding the costs of the guns. Even so, construction of the battery was a major feat of engineering, carried out under particularly difficult circumstances.
By 1944 the fortunes of the war were turning in the Allies favour, and the installation of the guns became less of a priority. Only two guns were installed in 1944-46 and 1948. The third gun was cancelled to save costs.
The army never manned the battery except when equipment was being installed, the only army occupants being a caretaker and his wife the rest of the time. The battery camp which would have accommodated army personnel was never built and the guns were only fired once, in 1951. In 1957 the coastal artillery was abolished as a branch of the New Zealand army and the guns and equipment at Waiheke cut up for scrap in 1960-61.
The 9.2 inch CB battery at Stony Batter is one of only three built in New Zealand; others are at Whangaparaoa and Wright's Hill in Wellington.
A combination of good design and isolation has resulted in a remarkably good state of preservation. The extensive use of underground tunnels and connecting passages, and the adoption of existing civil rather than military designs, are unique in coast defence battery design. These distinctive features were due to shortages of reinforcing steel and concrete and were made possible by the soft rock at Stony Batter which could be dug relatively easily.
Stony Batter is considered to be an engineering heritage site of international significance. It has been registered as a Category 1 Historic Place.