The 100 Ton Gun is one of eight Victorian rifled muzzle-loading 17.72 inch guns, nicknamed The Rock Busters, that where designed and manufactured in Newcastle-upon-Tyne, by Sir W C Armstrong & Company in 1870.
The first four were sold to the Italian Navy for mounting on their battleships Caio Duilio and Enrico Dandolo. This alarmed the British Government who, worried that their important Mediterranean bases might be defenceless against long range bombardment, commissioned four more. Two each for Malta and Gibraltar.
Today only two survive: One at Fort Rinella on Malta, which is still fired once a year, and the other here at the Napier of Magdala Battery. The former has lost its steam engine and hydraulic system, making Gibraltar's the best preserved example of this early 'Super Gun'.
Gibraltar's other 100 ton gun was mounted at the former Victoria Battery just off Grand Parade. Part of this site is now the City Fire Brigade HQ built in 1934. Rumour has it that some of the below-ground infrastructure still survives and is used for training purposes.
The Napier of Magdala Battery was constructed between 23rd December 1878 and 31st March 1884 on the site of the old 2nd and 3rd Rosia Batteries at a cost of £35,717. It was named after the governor during this period, Lord Napier of Magdala.
Ironically it was completed in the same year that Sir Andrew Noble, one of Sir William Armstrong's men, invented the significantly more powerful Smokeless Gun Powder.
This new powder needed longer gun barrels for its full powers to develop. So a new breed of breech loading weapons came into use; smaller calibre but with a much more devastating effect than any of the old black powder guns. Thus the 100 Ton gun was rendered obsolete without ever firing a shot in anger.
It is interesting to compare this gun with its range of 5-8 miles tops, with the 9.2" gun at O'Hara's Battery, installed only 17 years later. This had an, altitude assisted, range of over 16 miles.
Nevertheless, the site remained strategically important and four 3.7 inch anti-aircraft guns were installed during the Second World War, one of which remains.
Although basically a huge cannon, moving, loading and cleaning such a big weapon by hand would clearly be impractical. A steam-powered hydraulic system was therefore employed, both to move the gun and to operate the 45 feet long powered ramrods.
There were two loading chambers, used alternately, on opposite sides of the battery to allowing the gun to fire a round every four minutes. This needed a team of 23 men. However, by using only one loading chamber, a detachment of 15 men could manage at half the normal rate of fire.
A detachment under the command of one Lieutenant Colonel Outlive managed reduced this time to two and a half minutes, which may have contributed to the original barrel splitting. It was replaced with the barrel from the strategically less important Victoria Battery site.