 Cowes Castle , also known as West Cowes Castle , is a Device Fort in Cowes on the Isle of Wight . Originally built by Henry VIII in 1539 to protect England against the threat of invasion from France and the Holy Roman Empire , it comprised a circular bastion , flanking wings and a keep , and in 1547 it housed 17 pieces of artillery . With its companion fortification at East Cowes , the castle overlooked the entrance to the River Medina , an important anchorage . The invasion threat passed but the fortification continued in use until the middle of the 19th century , very briefly seeing action in 1642 during the English Civil War . 
