In Tudor times the coastal defences were strengthened (as by Henry VIII at St Mawes) and also at the time when a Spanish invasion was expected in the 1580s. Polruan also has a blockhouse fortification that guards the entrance to the river Fowey, one of a pair — its partner being situated on the Fowey side of the river. Between the two blockhouses was strung a defensive chain to prevent enemy ships entering the harbour, the chain being lowered for friendly vessels. This was primarily used during the wars with the Dutch. Many Napoleonic forts were built during the Napoleonic War in South East Cornwall to protect Plymouth Sound and Plymouth's docks in Devonport, Devon from attack: some are still in use today by the Ministry of Defence.