That absence is itself the point. Battery No. 12 at Glasthule, once armed with three 24-pounder guns and one 18-pounder gun and enclosed within a rectangular walled compound, has left no surface trace whatsoever. The site it occupied is now beneath the footprint of the baths building, which appears on the Ordnance Survey six-inch map of 1863 in precisely the place the battery had occupied on the equivalent map of 1837. The 1837 edition shows a walled enclosure with a narrow rectangular building along its western side, sitting roughly 140 metres north of the Martello tower and south of the Royal Victoria Baths. By 1863, the battery had been erased entirely.

The structure belonged to a coordinated chain of coastal defences thrown up along the east coast of Ireland during the Napoleonic Wars. In 1802, Admiral James Hawkins-Whitshed was appointed naval adviser to the Lord Lieutenant of Ireland, tasked with organising sea defences against a possible French landing. The following year he became Commander-in-Chief of the Sea Fencibles, the naval defence organisation in Ireland, and advised Lord William Cathcart, Commander in Chief in Ireland, on where the towers should be sited. Construction of the Dublin area Martello towers, squat circular fortifications designed to resist artillery fire and obstruct an invading force, began in September 1804 under Lieutenant-Colonel Benjamin Fisher of the Royal Engineers. By the end of 1806, all 26 Dublin towers and their associated batteries had been completed. The battery at Glasthule was one of that network. Its obsolescence came quickly. By 1842, the Commissioners of Kingstown Harbour were writing to the Board of Ordnance to describe Battery No. 12 as being in a state of complete dilapidation and noting, with some bureaucratic frankness, that it was rather an obstruction. They requested that the land be transferred to the Harbour Commissioners, pointing out that far better defensive positions existed at the pier heads and at Sandy Cove Point.

Visitors to Glasthule today will find the restored baths building occupying the site, with the Martello tower still standing a short distance to the south. There is no marker or memorial to the battery, and nothing on the ground to indicate what once stood there. The 1837 Ordnance Survey six-inch map, freely accessible through the OSi historical map viewer online, gives the clearest sense of how the battery was laid out relative to its surroundings. Taylor's map of the environs of Dublin, published in 1816, also shows the position of the tower and battery within the broader coastal landscape of the period. The Martello tower itself, recorded as DU023-017 in the national monuments register, remains the most visible reminder that this quiet stretch of shoreline was once considered a plausible landing point for an enemy fleet.