The dockyard at Portsmouth was founded by Henry VII, developing into a naval base that was essentially the nation's most important military establishment. Here, in times of war, huge fleets were assembled and the harbour that lay alongside the dockyard witnessed the constant arrival and departure of ships engaged in convoy duties, blockading and attacking enemy ports or intercepting hostile seagoing fleets. In turn, it was a potential target for an enemy, for if the dockyard could be destroyed or captured, then the nation's first line of defence, the Royal Navy, would cease to be effective. Sensitive to such a danger, successive governments built defence structures in and around Portsmouth as well as barracks to house the navy, army and marine personnel. As the firepower of guns increased and the nature of fortifications changed, so did the defences of Portsmouth, with these gradually pushed further and further back so that the forts and gun batteries would always ensure the safety of Portsea Island from either land or sea attack. In the twentieth century the defences were adapted further for the new threat of aerial bombardment or attack by submarine. This book will be of interest to all those who would like to know more about Portsmouth's remarkable military history.