The Maunsell Forts are armed towers built in the Thames and Mersey estuaries during the second world war to help defend the UK. They were operated as army and navy forts, and named after their designer, Guy Maunsell (Maunsell also designed forts for anti-aircraft defense). These were larger installations comprising seven interconnected steel platforms.The forts were decommissioned in the late 1950s and later used for other activities including pirate radio broadcasting. One of the forts is managed by the unrecognized Principality of Sealand; boats visit the remaining forts occasionally, and a consortium called Project Redsands is planning to conserve the fort situated at Red Sands. The fort was subsequently declared unsafe, and Red Sands Radio has moved its operations ashore to Whitstable. The design of these concrete structures is equal to a military grade bunker, due to the ends of the stilts, (under water) that are solidly locked into the ground. Many species of fish live near the forts because the forts create cover. They have provided landmark references for shipping. Previously, forts had been built in UK rivermouths etc. to defend against ships, such as the Grain Tower Battery at the mouth of the Medway dating from 1855, Plymouth Breakwater Fort, completed 1865, the four Spithead Forts:Horse Sand Fort, No Mans Land and St Helens Fort which were built 1865-80; and Spitbank Fort, built in the 1880s, the Humber Fort on Bull & Haile Sands, completed in late 1919, and the Nab Tower, intended as part of a WW1 anti-submarine defence but only set in place in 1920.