Following overland tests at Salisbury Plain during March 1897, on May 13, 1897, the Italian born and recently British based inventor, best known for his development of a radiotelegraph system, Guglielmo Marconi, assisted by George Kemp (who was a Cardiff based Post Office engineer) transmitted and received the first wireless signals over open sea between Lavernock Point and Flat Holm island.
The very first message transmitted in morse code was "ARE YOU READY". This was immediately followed by "CAN YOU HEAR ME" to which the reply was "YES LOUD AND CLEAR". The morse recording slip for the first message is on display in the National Museum of Wales.
Following the initial opening exchange there followed detailed technical messages in both directions indicating each end's equipment settings and receiving sound levels. Marconi indicated that he was using a spark on his equipment.
The successful test followed several days of trials and failure while adjustments were made to aerial length. Extensive trials were carried out over the remainder of the week in various weather conditions and with different settings on the equipment at each end. Marconi benefitted from the active encouragement of then Mr. William Preece (later Sir William Preece) who was Engineer-in-Chief of the Post Office and had himself transmitted radio telegraph morse signals across Coniston Water eight years earlier. Preece had been previously acted as a consultant to the Bristol Corporation's Electricity Department between 1883 and 1893. The Post Office engineers, including George Kemp who kept a detailed diary of these events, had been experimenting for some months at Lavernock Point. Kemp recorded the following in his diary of the experiments:
Marconi's new equipment was therefore used in conjunction with that already adopted by the Post Office. The initial tests were so successful over the three and a third mile (6 kilometres) stretch of water that it was quickly decided to relocate the telegraph equipment from Flat Holm to Brean Down Fort, near Weston Super Mare increasing the distance to nearly ten miles (16 kilometres) from the Lavernock Point transmitter.
Following these successful trials, Marconi subsequently vested his new patent rights in his 'Wireless Telegraph and Signal Company', which unfortunately prevented any further co-operation with the Post Office engineers. However George Kemp immediately resigned from his Post Office position and joined Marconi's new company as head of engineering development.
In 1948, to mark the 50th anniversary of the experiments, a bronze plaque was unveiled by the Cardiff Rotary Club inside the courtyard of the recently closed church of St.Lawrence, Lavernock, commemorating the historic radio transmissions over nine miles (14 km) of open sea. The small stone hut that Marconi used to contain his experimental radio telegraph equipment still stands on the cliff edge at the end of the lane near Lower Cosmeston farmhouse.
From the late 1890s until 1968 Lavernock and the nearby bays of St Mary's Well and Swanbridge (with its low tide walk out to Sully Island) were popular and busy holiday locations for regular day trippers from the South Wales Valleys, Newport, Cardiff, Penarth and Barry and the beaches were packed with visitors on most weekends and Bank Holidays throughout the summer. The hundreds and sometimes thousands of holidaymakers were served refreshments by an ice cream parlour, two busy cafes, the Golden Hind public house and the three star Lavernock Bay Hotel. Very few visitors arrived by car until the 1960s with the majority travelling by the half-hourly steam trains that stopped at Lavernock and Swanbridge Halts on the busy Taff Vale Railway Line en-route to Barry Island.
Lavernock started settling back to quiet seclusion in the early 1970s when the railway line had closed down under the Beeching Axe. Some modern day trippers arrived by car, to the degree that the lanes and the Swanbridge car park were often jammed, but visitor numbers had dropped off to such a degree that falling profit margins meant all the food outlets, the Golden Hind pub and eventually even the Bay Hotel closed down and the decline was accelerated even further.
A line drawn between Lavernock Point and Sand Point, Somerset marks the lower limit of the Severn estuary and the start of the Bristol Channel. Because of the extreme tidal range there are very strong currents or rips close inshore to the point with speeds that exceed 7 knots (13 km/h) for several hours at each tide.
Various proposals have been put forward to construct a Severn Barrage for tidal electricity production from Lavernock Point to Brean Down in Somerset and the provision remains under discussion by the various agencies.
On the point in the late 1860s Lavernock Fort gun battery was built by the Royal Commission and completed in 1870, with three 7" muzzle loading cannons to protect the channel approaches to Cardiff and Bristol shipyards during the short lived war between Britain and France that followed the French Revolution. Sometime before 1895 the gun battery was reinforced with a fourth cannon only for all four guns to be replaced eight years later by two rapid fire six inch (152 mm) former naval guns in 1903.
A two unit searchlight battery was added during the Second World War. The World War II gun emplacements formed part of the Fixed Defences, Severn Scheme and protected the Atlantic shipping convoy de-grouping zone between Cardiff, Barry and Flat Holm. Today the remaining main section of the gun battery has been listed as an Ancient Monument, which includes the gun emplacements, director-rangefinder observation position, crew and officers quarters. The structure is still commemorated through Lavernock Point's main access road being named 'Fort Road'.
In early 1962 a protected nuclear fallout shelter (or bunker) was completed at Lavernock Point for the ROC (OS Grid Ref: ST 1858 6903), who by the 1960s had switched from above ground aircraft spotting to underground operations with instruments to detect nuclear explosions and warn the public of approaching radioactive fallout in the event of nuclear war. The post members were mobilised later that year and volunteers spent nearly ten days underground during the Cuban Missile Crisis as the government prepared the country for potential outbreak of war.
The Lavernock nuclear bunker was closed down and abandoned by the ROC in 1975 after repeated destructive break-ins by local vandals, but the concrete entrance hatch and ventilator tower can still be observed next to the cliff walk near Lower Cosmeston farmhouse. The Royal Observer Corps itself was disbanded in December 1995 after the end of the Cold War and as a result of recommendations in the governments Options for Change review of UK defence.
Lavernock railway station was sold off and now forms part of the current caravan park. Long sections of the old railway track bed are still open from the Fort Road bridge as far as Lower Penarth as a rural greenway and cyclepath, however the track bed in the direction of Sully is either overgrown and impassible or has been sold into private ownership.
Lavernock, St Mary's Well Bay and Swanbridge (Sully Island) can still be reached along the clifftop path from Penarth.
The old cafe car park at Swanbridge was developed as part of the newly opened Captain's Wife public house in the mid 1970s.
The whole area continues to be redeveloped as several private caravan parks and holiday camps over recent years, the largest and longest established of which is the Marconi Holiday Village run by the Lavernock Point Holiday Park with chalets, fixed caravans and touring berths. The licenced Marconi Club at the holiday village is open to non-residents.