By 1822 the fort was the site of a semaphore station on the semaphore line from London to Portsmouth. It was constructed here to avoid the smog of the town of Portsmouth which would impede direct optical communications from Portsdown Hill. The fort was out of use as a defensive fort by the 1820s and in 1827 part of the fort fell into the sea. The semaphore station was closed in 1847 when the electrical telegraph took over.