During the 1860s, the British were concerned at the increasing strength of iron-clad ships, especially those of the French fleet across the channel. The heaviest Armstrong rifled breech-loader, the RBL 110-pr (7-inch) had not come up to expectations. As Armstrong himself had foretold, his system was not entirely suitable for heavy guns; the muzzle velocity of the 110-pr was not high enough to defeat the warships' armour - and the breech mechanism would not stand any increase in propellant charge to make it higher. Priority was therefore given to the construction of the heavy natures of RML guns which began with the recommendation of the ordnance Select Committee which sat in 1866.

Four systems of construction ensued; the 'original' followed Armstrong's 'built-up' system, the superiority of which had been duly recognised by the Committee. Subsequently, three other systems evolved, the 'modified', 'Fraser' and 'Royal Gun Factory' (RGF), incorporating improvements in strength and simplicity, but all retained the same basic principles, ie a steel 'A' tube over which other tubes and/or fittings of wrought iron were shrunk.

Guns included the 64-pr 64-cwt, 7-inch 4½- 6½- and 7-ton, 8-in 9-ton, 9-in 12-ton, 10-in 18-ton, 10.4-in 28-ton, 11-in 25-ton, 12-in 35-ton, 12.5-in 38-ton etc up to 17.72-in 100-ton. The New Zealand Government bought eleven each of the 64-pr 64-cwt and 7-in 7-ton guns in 1878 at the time of the 'first Russian scare'. However, by the time they arrived here in 1879 the 'scare' had passed so they were put into store and apparently forgotten until the next 'scare' in 1885 when they were mounted 'in all haste' (to quote the Fort Record Book). The Kiwi she's right attitude is older than you think!

Manufacture of the Mark 3 gun began in 1867 although the guns received in New Zealand in 1879 were made in 1878. It differed from earlier marks mainly in having fewer parts. It is built up of four portions, ie the 'A' tube of steel, the breech coil to which the trunnion piece is welded before being shrunk on the gun, the 'B' tube, and the cascable screw, all of wrought iron. On the right of the cascable is a gas escape leading to the end of the 'A' tube. The bore is rifled with three plain grooves on the Woolwich system with a uniform twist of one turn in 40 calibres. Full charge was 8 pounds of powder, MV was 1390 fs, range 4000 yards. The 64-pr was not designed for the defeat of armour but rather to attack the upper works of ships.

To digress from technicalities for a moment, two of the 17.7-ton guns mentioned above were installed at Gibralter - and thereby hangs a tale. During a practice shoot one of the guns misfired, and was ordered to be unloaded. What had happened to the 'instrument extracting projectile' supplied for the purpose is not recorded, but a small Drummer Boy - having been assured 'it was perfectly safe' - was persuaded to crawl down the barrel and attach a rope to the shot. When he crawled out legend has it he was immediately promoted to Corporal!