National Archives records reveal that worked started on this Magazine on 29th July 1870 and that the work was completed on 31st March 1873. Interestingly there is talk of Authority for Strengthening, so it is possible there was some sort of Magazine at this location already.
The cost of this work is given as £1,772, over the estimated cost of £1,598.
The Magazine had a capacity of 500 barrels of powder.
There is another magazine, built later, which lies adjacent to this older feature.