English: Maunsell Fort tower. Architect Guy Maunsell's amazing solution to a gap in aerial and naval defences during World War 2 was a series of forts, built several miles out in the Thames estuary. A testament to the resilience of the design structure, many still stand today, though these days there are also many signs that the elements are starting to take their toll. Almost all offshore oil rigs have since been based on these structures. Originally the towers were linked with walkways but these were demolished or fell into the sea when they became unstable. The remnants of a walkway can be seen between the tower in the foreground and the one to the left - this is a more recent addition and even this has decayed to the point that only two ropes remain.