Netley Castle is a former artillery fort constructed in either 1542 or 1544 by Henry VIII in the village of Netley, Hampshire. It formed part of the King's Device programme to protect against invasion from France and the Holy Roman Empire, and it defended Southampton Water near the Solent. The castle included a central, stone keep with two flanking gun platforms and was garrisoned by ten men. It was decommissioned during the English Civil War and by 1743 it was overgrown and in ruins.