These Treaty Port installations, including Fort Carlisle, were handed-over to the Irish authorities in 1938.

[19] By the mid- to late-20th century the CDA was merged into other artillery regiments of the Irish Army, and the fort primarily used as a training site.

The site remains in the ownership of the Department of Defence and is used by the Irish Army for exercises,[20] ceremonial "gun salutes"[21] and other training purposes.

[4] On the landward side, a dry-moat, ramparts, terreplein, caponier and flanking batteries defended the approaches.

The star shaped landward defences included three musketry caponiers, and a simple terreplein with movable guns.

These batteries were built with a number of underground shelters, vaulted magazines, and linked in places by bunkered tunnels.