Port Elizabeth has arguably the most complete collection of surviving coast artillery buildings and equipment dating from the Second World War (1939-45) of any port in South Africa. Before the Second World War the Port Elizabeth Harbour actually had no defence in place except for Fort Frederick which was built in 1799 to guard the original landing place in the early days long before a harbour was even built. In 1942 it was decided to put harbour defences in place at all South Africa's harbours. Three Fortress Observation Posts (FOPs) were built at Amsterdam Hoek (Bluewater Bay), Seahill (Cape Recife) and Skoenmakerskop, together with a Port War Signal Station next to Cape Recife lighthouse. These three along with the Algoa Battery building in Humewood and the Battery Observation Post on Brookes Hill had to keep a constant lookout for approaching ships, submarines and planes. The buildings were all constructed with curvy, free-form profile of parapets, angle buttresses and 'fins' to break up their square, box-like shapes when seen from the sea against the background of the bush.
The FOP in picture is the one in Cape Recife which can be visit while doing the Roseate Tern Trail through the reserve. Visit the South African Military History Society website for a lot more detailed information on this.