
Tower 18 was undermined and washed away sometime after Tower 17, but before the Second World War.1 A photograph of Tower 17 collapsing with Towers 18-21 behind it (seen right) was printed in 'The Navy and Army Illustrated' in 1903.2
As with Towers 16 and 17, the remains were said to still be visible during the 1970's,3 although as public access to the area is strictly denied, any surviving remains cannot be visited.