The first permanent fort at Tilbury was a D-shaped blockhouse built in 1539 by Henry VIII and first called the 'Thermitage Bulwark', because it was on the site of a hermitage dissolved in 1536. The Tilbury blockhouse was designed to cross-fire with a similar structure at New Tavern, Gravesend. During the Armada campaign the fort was reinforced with earthworks and a palisade and there was a boom of ships' masts, chains and cables stretched across from Thames to Gravesend anchored to lighters. Furthermore, it was in nearby West Tilbury that Elizabeth I rallied her makeshift army as it awaited the Armada in 1588