At the end of the spit are Calshot Castle (built by King Henry VIII), an RNLI lifeboat, an NCI station, several slipways, a former Royal Navy and Royal Air Force flying boat station and Calshot Activities Centre. The neck of the spit is owned by New Forest District Council while the end of the spit is owned by the Crown Estate who lease it to Hampshire County Council.
The castle is a low, circular, stone structure and was armed with large muzzle-loading guns. Its purpose, when it was built in 1539, was to protect access to the important harbour at Southampton from seaborne attack, by France or Spain from the English Channel via the Solent.
Calshot Naval Air Station was originally set up in 1913. Its choice as a location for operating flying boats is clear: the landing area is sheltered by land on the three sides of Southampton Water and by the Isle of Wight, several miles away, on the fourth side. In 1929 and 1931, Calshot was the venue for the Schneider Trophy, an international air race for seaplanes.
The Spit was transferred to civilian control at the start of the 1960s.
The site is now the location of Calshot Lifeboat Station operated by the RNLI, yachts and the National Coastwatch Institution. The hangars are home to Calshot Activities Centre and house indoor climbing walls, artificial ski slopes and a velodrome.
The spit is a potential navigation hazard for ships entering Southampton Water, and vessels are guided by the Calshot Spit light float. This replaced a Trinity House lightvessel (LV 78) that was anchored off the spit and which until recently was a static attraction at the Ocean Village marina in Southampton. In November 2010 it was moved a short distance to the Trafalgar dock where, after renovation, it will be displayed at the Aeronautica attraction, due (tentatively) to open in 2015. It was built in 1914 by J I Thornycroft shipyard in Southampton and decommissioned in 1978.
LV 50, which was once on the Calshot station, was bought by the Royal Northumberland Yacht Club, and remains their club ship to this day.
Historically the site's status as a military base provided a degree of protection for the local flora. The large scale constructions of car parks, beach-huts and the importation of topsoil has significantly reduced the range of plants present. Crambe maritima (sea kale) still grows on the spit and in the 19th century it was apparently harvested for sale in Southampton.
- OS Explorer Map, New Forest, Scale: 1:25 000.Publisher: Ordnance Survey B4 edition (2013). ISBN 9780319241509
- "Zone 8: Calshot Spit". nfdc.gov.uk. New Forest District Council. February 2004. Retrieved 31 October 2013.
- Chatters, Clive (2009). Flowers of the Forest Plants and people in the New Forest National Park. WILDGuides. pp. 177–180. ISBN 9781903657195.
- "Trinity House LV No. 78 Harbour Lights". Retrieved 2 July 2006.