page_title: Device Forts
section_title: Architecture
hierarchical_section_title: Device Forts / Early history and design / Architecture
caption_attribution_description: English: Defences of Gravesend and Tilbury. From the 1588 Thamesis Descriptio map. Reversed: North in the bottom!
context_page_description: The Device Forts, also known as Henrician castles and blockhouses, were a series of artillery fortifications built to defend the coast of England and Wales by Henry VIII. Traditionally, the Crown had left coastal defences in the hands of local lords and communities but the threat of French and Spanish invasion led the King to issue an order, called a "device", for a major programme of work between 1539 and 1547. The fortifications ranged from large stone castles positioned to protect the Downs anchorage in Kent, to small blockhouses overlooking the entrance to Milford Haven in Pembrokeshire, and earthwork bulwarks along the Essex coast. Some forts operated independently, others were designed to be mutually reinforcing. The Device programme was hugely expensive, costing a total of £376,000; much of this was raised from the proceeds of the Dissolution of the Monasteries a few years before.
  These utilitarian fortifications were armed with artillery, intended to be used against enemy ships before they could land forces or attack ships lying in harbour.
context_section_description: The Device Forts represented a major, radical programme of work; the historian Marcus Merriman describes it as "one of the largest construction programmes in Britain since the Romans", Brian St John O'Neil as the only "scheme of comprehensive coastal defence ever attempted in England before modern times", while Cathcart King likened it to the Edwardian castle building programme in North Wales.
  Although some of the fortifications are titled as castles, historians typically distinguish between the character of the Device Forts and those of the earlier medieval castles. Medieval castles were private dwellings as well as defensive sites, and usually played a role in managing local estates; Henry's forts were organs of the state, placed in key military locations, typically divorced from the surrounding patterns of land ownership or settlements. Unlike earlier medieval castles, they were spartan, utilitarian constructions. Some historians such as King have disagreed with this interpretation, highlighting the similarities between the two periods, with the historian Christopher Duffy terming the Device Forts the "reinforced-castle fortification".
  The forts were positioned to defend harbours and anchorages, and designed both to focus artillery fire on enemy ships, and to protect the gunnery teams from attack by those vessels. Some, including the major castles, including the castles of the Downs in Kent, were intended to be self-contained and able to defend themselves against attack from the land, while the smaller blockhouses were primarily focused on the maritime threat. Although there were extensive variations between the individual designs, they had common features and were often built in a consistent style.
  The larger sites, such as Deal or Camber, were typically squat, with low parapets and massively thick walls to protect against incoming fire. They usually had a central keep, echoing earlier medieval designs, with curved, concentric bastions spreading out from the centre. The main guns were positioned over multiple tiers to enable them to engage targets at different ranges. There were far more gunports than there were guns held by the individual fortification. The bastion walls were pierced with splayed gun embrasures, giving the artillery space to traverse and enabling easy fire control, with overlapping angles of fire. The interiors had sufficient space for gunnery operations, with specially designed vents to remove the black powder smoke generated by the guns. Moats often surrounded the sites, to protect against any attack from land, and they were further protected by what the historian B. Morley describes as the "defensive paraphernalia developed in the Middle Ages": portcullises, murder holes and reinforced doors. The smaller blockhouses took various forms, including D-shapes, octagonal and square designs. The Thames blockhouses were typically protected on either side by additional earthworks and guns.
  These new fortifications were the most advanced in England at the time, an improvement over earlier medieval designs, and were effective in terms of concentrating firepower on enemy ships. They contained numerous flaws, however, and were primitive in comparison to their counterparts in mainland Europe. The multiple tiers of guns gave the forts a relatively high profile, exposing them to enemy attack, and the curved surfaces of the hollow bastions were vulnerable to artillery. The concentric bastion design prevented overlapping fields of fire in the event of an attack from the land, and the tiers of guns meant that, as an enemy approached, the number of guns the fort could bring to bear  diminished.
  Some of these issues were addressed during the second Device programme from 1544 onwards. Italian ideas began to be brought in, although the impact of Henry's foreign engineers seems to have been limited, and the designs themselves lagged behind those used in his French territories. The emerging continental approach used angled, "arrow-head" bastions, linked in a line called a trace italienne, to provide supporting fire again
caption: 18th-century engraving  of a 1588 map showing the mutually reinforcing defences along the River Thames, including Milton and Gravesend blockhouses (top), and East Tilbury and West Tilbury blockhouses (bottom)[c]
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