A Henrician artillery castle, built in 1542-5 by Sir William Paulet for Henry VIII to guard the anchorage at Southampton Water. It was built as part of the network of coastal defences to defend England against the threat of French and Spanish invasion. It was maintained and garrisoned until at least 1626-7 and possibly as late as 1642. In the early 19th century the fort was converted a private residence and in 1840-60 it was modified and a Gothic tower built. It was extensively altered in 1885-90 and the castle became a convalescent home in 1946. In 2001 the castle was converted into apartments.
Close to Netley Abbey on the shore was another small fort, built by Henry VIII. at a late date, to protect the approach to Southampton, and prevent a landing at that part of the coast opposite to the town. In March 1627, the staff of this fort, called “Westoun Fortress”, consisted of a captain at 3s. daily pay, two soldiers at 6d., a porter at 8d., and six gunners at 6d., the annual cost being £103 8s. 4d.
It stood upon a little hill, now secluded among trees, and held two small platforms; in rear is a modern cottage attached to it. The tower is the addition of a late proprietor, who took the idea from one of Horace Walpole’s letters, recommending such an adjunct to render the fort habitable.
The castle is only about 200 yards from the W. entrance of the abbey, and seems to have been built on the site of the water-gate of that institution; there is a connecting passage between the two still existing, which, beginning in the abbey kitchen, opens into the castle grounds above the house. The walls of Henry VIII.’s fort, 9 to 12 feet thick, and upwards of 15 feet in height, are to be seen within the present house, having been hollowed out and pierced in the construction of the dining-room there, and two blocked-up doors are said to be traceable in the cellars, as likewise are the moat and earthworks along the whole front of the garden and carriage drive. This gatehouse has undergone so much change, first when transformed into a fort by Henry VIII., and afterwards in its conversion into a private residence, that it retains little of its original form. (Castles Of England, Sir James D. Mackenzie, 1896)