The North Head disappearing gun

The gun at South Battery is an 8 inch disappearing gun, so named because the shell it fired was 8 inches in diameter, and the gun was designed to ‘disappear’ between shots. It was built in 1886 at the Elswick Ordinance Works in England. 

The idea of the disappearing gun was that it retracted below ground between shots so it could be loaded out of sight of any attacking ships. It did this using the power generated by the recoil of the gun as it fired.

The gun was installed on the top of North Head in 1887 and was brought to South Battery in 1953 to replace an identical gun scrapped in the 1920s. It was put here to form part of a war memorial to gunners who died on overseas service.

There are very few of these guns left anywhere in the world and this particular model is very unusual as it was only ever used in New Zealand and Australia.

Facts

• The barrel of the gun weighs 13 tons and the mounting weighs 23 tons. 
• The gun and its mounting were dragged up the side of North Head by steam winch and then manhandled into position. 
• It fired a 95 kg shell using a 50 kg explosive cartridge. 
• The range of the gun was about 2500 m. 
• The shell could penetrate 350 mm-thick ship’s armour at about 1000 m range.

How did it work?

As the gun fired the recoil pushed the gun backwards and downwards into the pit. This in turn pushed the big bronze shaft under the gun into the lower cylinder where water and air were compressed through a series of valves. The compressed air was stored in the cylinder.

The gun was then reloaded and aimed while still out of sight of the enemy.

Aiming was done by moving the gun around using the two big hand wheels on the front half of the mounting and moved up and down by the two wheels on the side.

Orders on where to aim came down from the Observation Post by speaking tubes. The observation post is the little round structure with the cone shaped roof further up the hill. The speaking tubes were simply pipes down which the orders were called.

When the gun was ready to fire the pressure in the cylinder was released. This pressure pushed the gun back up to the surface. The gun was fired and the process started all over again.

How well did it work?

Yes it worked, but there were problems. The complicated mechanism meant the gun fired very slowly and the many valves often leaked, which meant the gun had to be pumped into position by hand.

Eventually people realized that ships found it very hard to hit anything as small as a gun which meant the gun could have been put out in the open and still have been safe from enemy fire. The wonderful disappearing mounting was not really needed. While fired in practice the guns have never had to fire at an enemy vessel.