Reasons for building the Towers and Batteries.
Since Theobald Wolfe Tone and the Society of United Irishmen attempted to rally France behind the Irish cause in the 1790s and with the coming to power of Napoleon Ireland was seen as the likely landing place for an invasion force. The Mouth of the Shannon was one of the three invasion areas ( the others were Galway and Bantry Bay) included in the French Directory’s instructions to Vice- Admiral Villaret de Loveuse in October 1796, during the preparations of an expedition to Ireland.This led to the British Admiralty constructing the a system of Signal Stations (51) as observation posts, together with 50 Martello towers, each maintaining a garrison of troops, officers and heavy artillery.
In addition to these a total of 10 quadrangular towers protecting batteries were built in Ireland between 1809 and 1817 on the coast in places that were particularly vulnerable to invasion. Seven were built to defend the River Shannon which was thought to be place the invasion was most likely to take place as it provided access to Limerick and the centre of Ireland. Six of these quadrangular towers were constructed along the shores of the Shannon Estuary below Limerick, Tarbert and Carrig Island on the south shore and Kilcredaun, Doonaha, Scattery Island and Kilkerrin on the north shore. The other one was built on the Upper Shannon to defend a ford at Keelogue below Athlone. Two others were built on the shores of Lough Swilly in County Donegal and one on Bere Island in Bantry Bay in County Cork.
Description of the Quadrangular Towers and Batteries
These Quadrangular towers were always to be found closing the gorge of a detached battery and were there to protect the battery from a landward side attack as well as cover for the battery of 24 pounder guns.
The batteries housed the gunners and the ordinary troopers. It was well defended by deep dry moats and was bombproof.All the 10 batteries formed a D-shaped enclosure in plan with masonry on the the scarp and counterscarp of the dry moat . Entrance to the batteries was across a drawbridge over the dry ditch or moat. The defensible guardhouses were entered from within the battery by a drawbridge slightly wider than the entrance doorway, over which the keystone bears the dates of construction. The guardhouses had basements or lower ground floors, level with the base of the dry moat in which it stands. The upper floor, level with the ground level of the battery, was approached by the drawbridge; above this floor level is the gun platform carried on the barrel-vaulted ceiling of the first-floor apartments.Musket-loops were provided at the lower levels, allowing for close defence of the moat in the manner of a caponnière. Musket-loops at the upper floor levels, were fitted with shutters on the outer face of the wall, commanded the interior of the battery. Other loops are arranged on the opposite side at this level, facing the approach to the rear of the battery on the landward side. On the roof-level gun platform, protected by broad parapets some six feet in height, were two guns mounted on traversing platforms: howitzers or carronades for defence of the landward side of the battery and they fired exploding projectiles. The traversing platforms, one at each end of the roof, enabled the guns to be trained through an angle of about 270 degrees, covering the ground on each flank of the battery and to the rear.
The main armament of the battery consisted of six 24-pounder guns mounted on traversing platforms, each revolving on a front pivot behind the inner face of the parapet.The range of the 24 pounder guns was 2km.Most of the guns could be simultaneously pointed at the same point. They fired either hot cannon shots to set fire to a vessel or cold shots to sink a vessel. The cannon shots were held in a bomb proof section within the barracks.
The batteries also provided protection for vessels anchored within range of their guns, otherwise vulnerable to attack by enemy ships of war or privateers. In 1804 the gunboat establishment in Ireland included five gun vessels in the Shannon Estuary armed with 18-pounder guns and 32-pounder and 18-pounder carronades. These small craft operating in the shallow waters of the estuary could not be pursued by deeper-draught vessels such as ships of the line or frigates.
Description of Tarbert Pentagon Tower and Battery.
The site of the battery and tower was on Tarbert Island. In 1841 the island had a population of 134 people , no trace remains. In the 19th Century the first road was built to connect the island to the mainland by Steam Navigation Company and the island is now part of the mainland and the whole historic site was demolished during the building of the ESB power station in the early 1970s.
The battery is shown by survey plans to have been bastion-shaped (pentagon) in plan with two faces overlooking the estuary to the north. The main armament was arranged behind these two parapets, with three guns to each and a centrally placed gun at the salient angle, giving seven pieces of ordnance in all. The battery was some 200 feet wide and had the usual arrangement of a defensible guardhouse in the rear. Entry to the battery was through an arched gateway about seven feet wide, presumably approached originally across a drawbridge over the dry moat. The battery was sited on the highest part of Tarbert Island; it is possible that it was one of the works under construction in 1794-95 or perhaps a partial rebuilding of one of these earlier structures. The defensible guardhouse was similar in dimensions and detail to those that survive in good condition at Kilcredaun and Kilkerin, suggesting a date of construction contemporary with them, between 1808 and 1814.
Tarbert battery was sited about forty feet above water level, towards the south-east side of the island; a late eighteenth-century painting of the Shannon depicts a battery with embrasures close to water level on the north side of Tarbert Island, which may be the battery of 1783 or a work built by Ferrier in the 1790s. In 1811 Tarbert was recorded as having thirteen guns, suggesting that this battery at water level or another work was in use in addition to the battery and defensible guardhouse described above.