What makes it quietly odd is not just its military architecture but its afterlife: at some point the whole complex was pressed into service as a store for fish boxes. Gun ports, originally the double-splayed openings designed to allow a wide field of fire while minimising the gap exposed to enemy shot, were later widened and fitted with window frames. A domed magazine tucked into the north-west corner, approached through a small ante-chamber, found itself in a structure that had effectively changed profession.

The battery sits at the end of a covered way leading from James' Fort, the larger fortification to the west. Dating the blockhouse precisely has proved elusive. A 1604 account for the construction of James Fort includes an allocation of £50 for a blockhouse at the point of the land, suggesting it was part of that building programme. O'Neil, writing in 1940, argued the earliest elements date to the sixteenth century, pointing to a narrow vertical slit in the passage wall as probable cannon provision from that period. Whatever its origins, the complex is shown on a 1625 map and appears clearly in Thomas Phillips's detailed prospect of the harbour drawn in 1685. The remains include two flanking structures on either side of a sloping entrance ramp, each with fireplaces and gun loops, as well as a rock-cut stairway rising to a small observation platform. About 80 metres to the west stands a separate roofless building with walls still at full height, ivy-clad and somewhat mysterious in its own right. Kerrigan suggested it may be the remains of a tower built between 1654 and 1656 and visible in the Phillips prospect, though the Phillips depiction shows a tall square tower quite unlike the present gable-ended structure. More intriguingly, four angled flues feed into a single chimney stack in a configuration that points less to domestic use than to fish-curing, a function confirmed by local tradition.