[mhandley]

The listing mentions a 30,000 gallon reservior, so I imagine rainwater collecion from the "parade ground".

[defrost]

That'd be my guess also: https://britishlistedbuildings.co.uk/300017169-thorne-island...

The British Listed Buildings site has photos of the fort and boat approach with stairs, picking crane, and sloped ladder lift for getting loads from water to gate.