What military developments were invented during the Great Siege?


An interesting experiment in artillery is what is known as ‘Healey’s Mortar’ which can be seen at the Ape’s Den on the Upper Rock. This consisted of a large, wide borehole into the Rock which was to be filled with gunpowder and small rocks. When fired the mortar would send these rocks showering down onto any attacking enemy. It is popularly thought that the mortar was a failure, when in reality it was simply never used because there was never an enemy landing along the red sands stretch of Gibraltar’s coast.

The fourteenth siege is famous for the experimental work carried out by British gunners. They hauled large cannon to the summit of the North face from where they could fire much further than those guns situated at Willis’s Battery. They also experimented with shells and bombs fired at the enemy.
Red-hot shot – these were employed as an incendiary device for burning the timbers of Spanish batteries. They would become invaluable against the Spanish floating batteries later in the siege.
Fuse lengths – bombs tended to bury themselves in the sand before exploding reducing their deadly blast. Captain Mercier found a way of combining a short fuse length with an exploding shell, which was calculated so accurately that they exploded in the air above Spanish work parties. This practice later evolved into shrapnel.

Illumination rounds – Captain Witham (after whom Witham’s Road is named) concocted a mixture which burnt brightly enough to detect Spanish working parties creeping forward at night. They were first called star shells; today we would call them flares.
Firebombs – set fire to Spanish batteries and wooden fortifications on the isthmus.
Koehler’s depressing carriage – Towards the end of the siege it was found that many of the Spanish trenches were too close to the British lines and north face and so could not be fired at due to the angle of fire. Lt. Koehler invented a depressing carriage which would allow the gun to be fired downwards and so hit Spanish working parties who had managed to get close to the Rock and were attempting to mine into it.

Fig.19. Courtesy Gibraltar Museum. Koehler depressing carriage as drawn by Lieutenant Koehler, 1782 . Courtesy Royal Artillery Historical Trust.

The Upper Galleries
As the siege continued, Spanish work parties, under cover of darkness, edged ever closer to prepare new batteries and trenches dangerously close to the British lines.
The Governor, General Elliot offered a reward to anyone who could tell him how to get guns onto a ledge on the northern face of the Rock known as the ‘Notch’ as from this vantage point they would be able to direct enfilading fire at the Spanish lines creeping closer to the Rock. Major Henry Ince, a member of the Company of Soldier Artificers, suggested that this could be done by tunnelling through the Rock. Permission was granted, and work started on May 25th, 1782.
The soldiers relied on brute strength, on their skills with a sledgehammer and a crowbar, and were also aided with gunpowder for blasting away the rock. In five weeks 18 men had driven a tunnel 25m into the Rock.
As work progressed, the dust from repeated blasting began to suffocate the miners, so it was decided to open a vent to let air into the tunnel. When they looked out they realised that from that position they could clearly see the enemy working parties below and so a cannon was placed from this opening to blast the enemy trenches.
Other firing points were cut and guns mounted, and, by the time the siege ended in February 1783, the tunnel was 113m long and had four guns mounted in it.
Work on the Galleries did not stop with the end of the siege, but continued to make their slow progress towards the Notch. The Notch was eventually hollowed out and a battery of seven guns was placed there giving the defenders a superb 180° arc of fire should Gibraltar ever be attacked by land again. The chamber was named St. George’s Hall, after the patron saint of England.
In gratitude to valuable services, Sergeant Major Ince was rewarded with a Commission and granted a plot of land on the Upper Rock which is still known today as Ince’s Farm. In addition, the Duke of Kent (Gibraltar’s Royal Governor and father of Queen Victoria) presented Ince with a valuable horse.

The simple grate for heating red-hot shot, after a drawing by G. Palao.