a more powerful diaphone fog signal was installed (in place of the old fog horn), which gave one 2.5-second blast every minute. It was synchronised with the radio beacon; by timing the delay between receiving the radio signal and the audible signal, vessels were able to calculate their distance from the tower. The tower was equipped with a fog bell, as well as the diaphone, which sounded one stroke every 7.5 seconds. The Nab Tower was manned as a lighthouse, but also functioned as a Royal Navy signal station; and during World War II it was equipped with a pair of Bofors guns to provide some defence to the Solent approach, and actually shot down several aircraft. The Royal Navy withdrew its personnel from the tower some time after the war, but the tower remained under Ministry of Defence ownership until 1984, when Trinity House acquired the freehold (they had previously taken over responsibility for the light itself from the Admiralty in 1929). The Nab Tower still functions as a lighthouse, but since 1983 it has been unmanned. That year, a helicopter pad was constructed on the tower and a new pre-fabricated lantern-tower was installed containing an automated acetylene lamp; as well as powering the lamp, acetylene gas drove the revolving mechanism for the lightweight GRP optic in which the lamp was set. In 1995 the light was converted to solar power operation and a new Orga rotating beacon was installed in the lantern (later a Vega VRB-25 rotating beacon was used). In November 1999, the merchant freighter Dole America, carrying a cargo of bananas and pineapples, hit the Nab. The ship was badly damaged and only avoided sinking by being run aground. The base of the tower suffered superficial and internal damage. The damage was repaired in 2001. The tower was featured as the main setting of the 1951 Hammer thriller The Dark Light. Major refurbishment in 2013 In 2013, Trinity House commissioned BAM Nuttall to undertake a major refurbishment programme due to extensive corrosion of the upper levels, meaning it was unsafe to land helicopters upon the helipad. Partial dismantling of the structure followed, undertaken with the help of a tower crane, which was installed within a former ammunition shaft. The height of the tower was reduced from 27 metres to 17, all external steel and cladding were removed and the existing concrete sub-structure was coated in a