Between 1866 and 1877 three 10-ins, 18 ton RML guns were installed in a casemated bastion. These positions had iron shields and iron roofs over the front part.
The installation of the cost cost over £6,234 with an additional £1,300 for the overhead iron cover.
These three guns worked in conjunction with the two two guns on Orange Bastion to provided overlapping fields of fire covering the inner harbour area just south of the Old Mole.
There are expense magazines on the gun platform.
During WW2 the embrasures were bricked up and concrete platform installed in the gun embrasures so that machine guns could be mounted from defence.
The whole are has recently been restored.