The island of Guernsey has been fortified for several thousand years, the number of defence locations and complexity of the defence increasing with time, manpower and the improvements in weapons and tactics.

Being in the front line of many wars, invasion was almost always a threat and the best locations for defence were being constantly rebuilt with older constructions being re-used and improved.

Early defences

The first form of defences comprised safe locations for the islanders to flee to in the event of an invasion. The headland at Jerbourg, the Castel fortress, the Chateau des Marais and the Vale Castle were probably the earliest.

The Jerbourg Point defences resembled an Iron Age fort, it comprises a series of ditches and banks across the neck of the headland, providing a short defensive wall behind which the people could retreat in times of danger. Dating from 2,000 B.C. the Jerbourg defence of three ditches was improved, firstly with stone reinforcing and later with wooden platforms, palisades and a tower, however it fell to French invaders in 1338. Nothing remains of the Castel fortress, apart from the parish name "Castel", or castle. It is suspected to date from Roman or Viking times and is thought to be located under the parish church. Chateau des Marais, also called locally "Ivy Castle" built in a swamp, a "marais", using the natural wetland, supplemented with banks and ditches for defence built in the 12th century. as a standard Motte and Bailey fort. The castle of Saint Michael or as it is now called "Vale Castle", dating from the Iron Age, was constructed to protect the population against pirates by providing a safe refuge. It is not possible to identify when the medieval works were started, possibly in the late 10th-century.

Castle Cornet was started in the late 13th Century on an islet accessible at low tide, outside Saint Peter Port. It would serve as the main base for the Governor of Guernsey, the commander of the Island's military forces, for many centuries.

The Guernsey militia was formed in 1337 and would continue until disbanded in 1946. It was compulsory for all men to belong to the militia. They trained weekly and for six centuries provided the main defensive force for the island.

A French invasion in 1338 captured the whole island including Castle Cornet, which dates back to at least 1256. Two years later the island was recaptured by English forces after the French navy was crippled at the Battle of Sluys and in August 1345 Castle Cornet was also recaptured. 13 years later the castle was again captured by the French before being evicted the following year.

In 1350 the King Edward ordered walls to be constructed around the town. The order was repeated when the work was not undertaken, but no evidence has been found of their existence. They would have linked the Tour Gand to the north with the Beauregard tower in the south.

In May 1372 Owain Lawgoch a claimant to the Welsh throne, at the head of a free company, on behalf of France, attacked Guernsey, popularly called "La Descente des Aragousais". Owain Lawgoch withdrew after killing 400 of the Island militia, The poem of the same name refers to the Vale Castle as the Château de l'Archange, the location of the last ditch stand against the insurgents.

With the advent of cannon and gunpowder, defences, now based mainly around Castle Cornet were remodelled between 1545 and 1548.

During the Third English Civil War, Castle Cornet, the main fortification in the island, supported the King whilst the island supported Parliament, this resulted in a siege of the castle that lasted nine years, ending in 1651. The castle had been improved over the centuries with added walls, gates and batteries.

The King's Survey of the Channel Islands was commissioned by Charles II in 1679. The report produced by Colonel Legge a year later was a comprehensive account of the state of defence, harbours and civil jurisdiction of the Islands. In Guernsey, defences had been poorly maintained, Castle cornet having suffered a major explosion after a lightning strike in 1672.

Main early defences, starting from St Peter Port and moving in a clockwise direction.

Parish Place/Name Notes Coordinates St Peter Port Castle Cornet ‡ £ Main defence, built on islet and constructed of granite St Peter Port Town Walls possibly built around 1350 St Peter Port Gand tower existed in the Pollet area, La Tourgand St Peter Port Beauregard tower built in 1357 on Mignot Plateau, now demolished St Martin Jerbourg headland ʘ earthen ditches and banks to protect headland Forest La Corbière Headland A clifftop fortification that had fallen into disrepair by 1680 Torteval Pezeries ‡ ʘ Fort first mentioned in 1680 Castel Hommet headland – Fort Hommet ʘ fortification recorded in 1680 with one gun Castel Inland fortress pre 600 A.D. possible earth and wood construction now demolished Vale Le Marchant headland – Fort L’Angle ‡ ʘ small fort mentioned in 1680, renamed in 1805 Le Marchant Vale Vale Castle ‡ ʘ built on top of a rock outcrop, protected by 15C granite walls St Sampson Chateau des Marais ‡ ʘ built in a swamp, a standard Motte and Bailey fort

Key ‡ Protected Monument £ Accessible with fee ʘ Accessible

18th and early 19th Century

18th Century threats from France

Having lived with constant threats during the Seven Years' War (1754–63), threats of an invasion from France during the Anglo-French War (1778–83) resulted in additional artillery being brought to the Island and the construction of several forts, numerous batteries covering possible landing sites and fifteen Guernsey loophole towers built between 1778 and 1779, The threat was real as an invasion of nearby Jersey resulted in the Battle of Jersey in Saint Helier in January 1781. Work started in 1782 on the massive Fort George, on the hill south of Town, it would take over three decades to complete. Guernsey granite was used for the majority of the gun platforms, forts and walls with embrasures often lined with brick.

A map was produced in 1787 for the Duke of Richmond as Master-General of the Ordnance to show all existing roads and military positions.

French Revolution and Napoleonic era defences

The French Revolution in 1789 added to the concerns in the Channel Islands and resulted in additional constructions and an increase in manpower.

The island militia of around 3,000 men provided both infantry and coastal artillery units. They were supplemented with regular British infantry battalions who rotated and were increased or reduced depending on the current threat to the island. Before the barracks were built in Fort George, islanders were required to provide accommodation for soldiers that could not be accommodated in Castle Cornet. Each Parish had its quota and if they were quartered in public houses or private dwellings, the parish authorities were liable for the cost. Non British units, which were not allowed on the UK mainland, were sometimes based in Guernsey, including from 1793 to 1796 French Royalists and in 1799, 6,000 Russian troops, who were quartered at Delancey. In 1796 Peter de Havilland, a Jurat was appointed superintendent of thirteen signal masts around the island, installed to give warning of approaching ships.

Lieutenant-General John Doyle was appointed Lieutenant Governor of Guernsey in 1803. After declaring a "state of emergency" in 1804, he undertook many works to improve the defence of the Island, including the draining of the Braye du Valle, improving some roads to military standard and building forts and batteries around the coast, including completing Fort George. Major-General Sir John Doyle was supported from 1810 by the new Bailiff, Peter de Havilland. The "emergency" lasted until 1815.

Doyle was instrumental in getting three Martello towers built in 1804–1805, as well as the reclaiming of Braye du Valle 1806–1808, the improved military roads with mile markers, for which he argued eloquently, against much opposition, and barracks which together gave the militia and regular units improved facilities to repel any invasion.

The Royal Navy provided the first line of defence, Captain Sausmarez, in command of a Guernsey-based squadron consisting of three frigates, HMS Crescent (1784), HMS Druid (1783) and HMS Eurydice (1781), a lugger, and cutter frustrated a planned invasion by 20,000 French soldiers of the Channel Islands scheduled for February 1794, due to his vigilant eye Admiral James Saumarez was again put in charge of a squadron based in Guernsey from 1803 to 1808.

Defences

Land based defences, starting from St Peter Port and moving in a clockwise direction.