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With The American War of Independence raging, France and Spain saw an opportunity to take advantage of Britain’s stretched forces. They allied themselves with the Americans and declared war on Britain. Their plan was to firstly capture Gibraltar, then invade mainland Britain.
Gibraltar was so strategically important that it became an obvious target for attack, so its defences were considerably strengthened. 1772 saw the formation of the Artificer Corps, forerunners of today’s Royal Engineers. These were soldier/tradesmen, combat troops also skilled in the construction of defence works. In 1777, Colonel William Green suggested further modifications to the defences, which included the construction of the King’s Bastion.
On 24th June 1779, birthday of King George III, hostilities began. The French and Spanish blockaded the port to stop supplies coming in, believing they would quickly bring the garrison to its knees, but this proved not to be the case. Despite outbreaks of scurvy and other sickness due to the lack of fresh food and constant bombardment by Spanish artillery, morale remained high under the leadership of the governor, General George Augustus Eliott.
The British position was improved with the arrival of two relief convoys, the first in January 1780 under Admiral Rodney and the second in April 1781 under Admiral Darby. They brought in much needed food, supplies and extra troops and evacuated some of the civilian population.
A further boost to British morale came in November 1781. The enemy were building new trenches and batteries on the isthmus, to bring their cannon closer to the town and inflict more damage. General Eliott ordered a sortie, so on the evening of 26th, 2,500 troops crossed the isthmus and attacked the Spanish lines. They destroyed 28 pieces of artillery and trenches, blew up magazines and inflicted heavy losses on the Spanish troops, at a cost of only four British killed. A Spanish logbook captured in the attack had already been filled in with the entry ‘nothing occurred this night’.
The siege saw two major advances for the British gunners. In February 1782, Lieutenant Koehler of the Royal Artillery first demonstrated the Depression Carriage he had invented. This allowed a cannon to be easily pointed down from high up on the North Face to fire down on the enemy below. The sheer nature of this North Face meant that some of the approaches could not be covered by the British guns, so in May a group of artificers under Sergeant Major Henry Ince started work on the first tunnel in Gibraltar. The original plan was to tunnel to a protruding rock called the Notch and place a cannon there, but during construction they opened up a small hole in the side of the tunnel to aid ventilation and realized that it would make a perfect gun embrasure. Eventually these Upper Galleries or Great Siege Tunnels would house 17 guns, completely covering the northern approaches.
In early 1782, under the leadership of the Duc De Crillon, French troops captured the island of Menorca from the British. He was then appointed commander of the siege of Gibraltar to give it fresh impetus. His aide, Colonel D’Arcon, came up with a plan for a massive amphibious assault on the Garrison, led by 10 floating batteries. These were specially adapted large sailing vessels, equipped with many cannon and thick walls to protect the crew. On 13th September the Grand Attack was launched. The batteries manoeuvred into line opposite King’s Bastion and began to pound the town. At first the British return fire was ineffective, but then they started to heat cannonballs in a furnace. These red-hot shot proved far better. By late afternoon the two main ships were on fire and by one in the morning they were abandoned and the other batteries set on fire so they could not be captured. This was a crushing defeat for the Franco-Spanish and the last major offensive of the siege.
A third and final relief convoy arrived in October under Admiral Howe and on 2nd February, 1783, a truce was signed with Britain keeping Gibraltar and the Franco-Spanish taking Menorca and parts of the West Indies and Florida.
The siege lasted three years and seven months and was the longest in British military history. The garrison of 7,000 was heavily outnumbered by 40,000 French and Spanish troops, but still managed to hold on. The number of enemy losses is not known exactly, but is considered very high. The British military lost 333 dead and 138 disabled through enemy action, but a further 536 died of sickness.