Alum Position Finding Station was designated a Station Number IV and appears to have had two cells and what is called a Fire Control Station. The date of building these positions is not known, but authority to build was given on 14th October 1891. The station was located on Headon Hill to the rear of Hatherwood Battery.
One of the two Position Finding, designated as the ‘C’ cell, was of similar design to one of the cells built at the same time at Totland Point Position Finding Station. There is no overall plan showing the layout of this Station.
The three positions were all of cut and cover construction with the viewing platforms facing North towards the sea approaches to the Western Channel entrance to Southampton and Portsmouth Harbours.
One of the original positions has been located but the other two are believed to be lost or otherwise inaccessible.
This position finding station is recorded in UK TNA WO 78/4294.