What they are actually skirting is a Napoleonic-era gun battery, designated Battery No. 11, capable of housing a garrison of 36 men and armed, at its peak, with one 68-pounder gun and five 8-inch smooth-bore guns arranged to command the bay to the west, north, and east. Each gun was mounted on a roller system to allow precise aiming. A shot furnace inside the compound was used to heat cannon-balls before firing, a standard tactic of the period intended to start fires aboard wooden ships. The battery's D-shaped enclosure, measuring roughly 34 metres east to west and 19 metres north to south and built from ashlar-cut stone, still stands on its headland more or less as it appears on the 1863 Ordnance Survey map.

The battery was one of three constructed to defend Dublin Bay, alongside those at Dun Laoghaire and Dalkey Island. Its origins lie in a reorganisation of Irish coastal defences prompted by the threat of French invasion during the Napoleonic Wars of 1803 to 1815. In 1802, Admiral James Hawkins-Whitshed was appointed naval adviser to the Lord Lieutenant of Ireland, and the following year he became Commander-in-Chief of the Sea Fencibles, the naval defence force in Ireland. Working with Lord William Cathcart, Commander in Chief in Ireland, Hawkins-Whitshed helped determine the siting of the Martello towers, the squat, thick-walled circular forts built across coastal Europe in response to the same threat. Construction of the Dublin-area towers and batteries began in September 1804 under Lieutenant-Colonel Benjamin Fisher of the Royal Engineers, and by the end of 1806 all 26 Dublin Martello towers and their associated batteries were complete. A magazine was added inside the Sandycove Battery later; work began on 1 October 1860 and was finished on 5 May 1861 at a cost of £599, designed to hold 100 cases or barrels of gunpowder. By 1870, Thom's Almanac recorded Master Gunner Thomas Birks as the officer in command. By 1883, the guns were listed as obsolete 150mm muzzle-loaders, and the site was functioning primarily as a militia artillery training facility.

The battery was demilitarised in 1896 and leased to the Dublin Bay Sailing Club for £30 per annum, which accounts for its current appearance and the difficulty of simply wandering in. The Martello tower associated with the battery, the one now known to Joyce readers the world over, stands approximately 70 metres to the south and is open to the public as a museum. For those interested in the battery itself, the ashlar perimeter wall is visible from the coastal path, and the general outline of the D-shaped enclosure can be appreciated from the headland. A path cut through the rocks, visible on an 1883 military plan, may represent the original rock-cut defences laid out when the battery was first built, and is worth looking for along the seaward edge.