Fort du Salbert Fort du Salbert , also known as Fort Lefebvre , was built between 1874 and 1877 . It was named after General François Joseph Lefebvre . It forms part of the Séré de Rivières system fortifications in the fortified region of Belfort in northeastern France . It is located at the summit of Salbert hill to the northwest of Belfort . During the early years of the Cold War it briefly served as an air defense coordination center . Séré de Rivières fort . Fort du Salbert is one of the second ring of forts around Belfort , built about 5000 to 6000 meters outside the first ring of the 1840s . All of the new generation of forts abandoned sheer walls and bastions in favor of low earth - covered mounds to better resist artillery . After it became apparent that masonry forts would not resist explosive shells , the fort was modernized beginning in 1885 with concrete over the caponier s and the creation of underground shelters for troops . From 1893 the fort was connected to other Belfort forts by the Chemins de fer du Territoire de Belfort strategic railroad . The fort was equipped with optical semaphores allowing communications with other forts . During the First World War a number of underground galleries were constructed to link the caponiers to the caserne . Fort du Salbert commands an area of ponds surrounding Malsaucy , and controls roads to Lure , Giromagny and the Paris rail line . Its initial construction cost was 2 , 120 , 332 francs d ' or . Initial manning was 460 men , 24 non - commissioned officers , and 13 officers . A well and cistern provided water . Armament in 1882 was five 155mm long gun s , eight 120mm long gun s , and a variety of small mortars and small - caliber guns for close defense . A 1900 modernization was to add a Galopin armored twin 155mm gun turret and an armored observation post . The gun turret project was abandoned , along with a further addition of a machine gun turret and a 75mm gun turret . The main fort never received the extensive concrete cover that was applied to other Séré de Rivières forts . During the quarrying of the fort ' s stone the caves of Cravanche were discovered in 1876 . NATO Ouvrage " G " . Introduction . It ' s located here : . From 1949 to March 10 , 1967 , France ' s military operated within the NATO command structure , integrating its air defense system ( the " Défense Aérienne du Territoire " ( D . A . T . ) ) with that of NATO through the indirect use of American aid funds . Between 1953 and 1958 , the D . A . T . built a radar station in an old troops shelter ( in French : " abri - caverne " ) near the fort , called " Ouvrage " G " " . Called " " Station Maître Radar 60 / 921 " " , it was used beginning in 1959 , covering an area on the surface of three times the area of the troops shelter . Ouvrage " G " complemented " Ouvrage F " , another D . A . T . station located at the old Fort François de Guise at Metz , while " Ouvrage H " was established as " Base aérienne " 901 Drachenbronn / " Station Maître Radar 50 / 921 " in the former Maginot Ouvrage Hochwald . Ouvrage " G " was equipped with seven radar antennas installed on top of the fort . The principal radars are presently located on the Ballon de Servance . The military vacated the Fort de Salbert in 1972 and removed the antennas from the fort . The city of Belfort took possession of the site . The foundations of the radars and the fort ' s heating oil tanks remain . In 1990 Belfort concluded an agreement with an association without lucrative purpose named " Les aventuriers de l ' histoire " to restore the site . The volunteer group cleaned , repaired , and worked to make the site ready for public visitation . The group ' s enthusiasm was tempered by repeated setbacks , culminating with the explosion of several improvised bombs on the site which released asbestos and made the site unusable for the public or for restoration work . By mutual agreement between the city and the volunteers , public access was discontinued and the " aventuriers " disbanded . Ouvrage " G " was closed , its doors welded shut . Description . Ouvrage " G " had four Alstom ( Tarbes ) 260 horsepower diesel generators , started with compressed air and provided with sufficient fuel for one month . In addition , it was provided with air conditioning and gas protection , designed to maintain an overpressure level to keep contaminants out . Blast doors were installed at personnel entrances . Six radar antennas and one microwave link to the Ballon de Servance were located on the fort ' s surface , with the electronic equipment in a room under each . The surveillance was managed from the central operations room . Arranged like an amphitheater , it was disposed on two levels of booths focusing on three map display tables : A map of the territory concerned was attached to each table . Markers were placed on the table to represent planes and associated information , moved about on the table by attendants with poles . The operations room included a balcony for the observers who would transmit directions to the forces outside . Opposite the booths , four tote boards were placed on the walls : Booth assignments included those dedicated to identification , electronic countermeasures and three interception control stations . Other rooms that did not overlook the control room were provided for weather and technical control . The detection room housed the radar scopes showing the image generated by the radar system . The system used triangulation to establish the position of radar targets . Ouvrage " G " was provided with three telecommunication networks : Security for Ouvrage " G " was provided by personnel from Luxeuil Air Base . While the facility was designed for 500 occupants , it was in reality occupied by about 350 . During its period of operation the nature and details of the base were secret . In 1959 operations at Salbert were terminated and the force reduced to maintenance and security , with the surveillance function detailed to Ballon de Servance . The station had been fully operational for scarcely two years . The station was decommissioned due to the obsolescence of its radars , whose short range , low altitude coverage and poor performance made them of limited use . Consolidation and automation of radar surveillance made the Salbert facility obsolete . The station was fully maintained in operating order until 1972 , when it was turned over to Belfort . In 1966 Radiodiffusion - Télévision Française ( RTF ) placed a television transmitter on the site . In 1969 a relay station for Air Force communications was installed at the fort . In the summers of 1969 and 1970 the barracks were used as a military rest and recreational facility . In 1971 two receivers for the " service de transmission de l ' intérieur " ( S . T . I . ) were installed for the benefit of the prefecture of Dijon . After negotiations with the Army , the city of Belfort purchased the Fort de Salbert in 1972 . During the summer and autumn of 1972 , military engineers salvaged machinery and materials from the site . The barracks were dismantled . Belfort took possession on October 15 , 1972 . After the city took possession the site became a popular recreation area . In 1978 the city decided to redevelop the summit . Work began the same year and was finished in 1983 . A P . T . T . tower was placed on the site in 1976 .