Fort de Dailly The Fort de Dailly is the largest component of Fortress Saint - Maurice , which is in turn one of the three principal fortified regions of the National Redoubt of Switzerland . Almost entirely subterranean , the Fort de Dailly was built in the Massif de Dailly to the east of Saint - Maurice beginning in 1892 . With the Fort de Savatan , it comprises a fortress complex encased in rock high above the strategic Saint - Maurice valley , capable of commanding the valley from Chillon to Martigny . It is the central component of Fortress Saint - Maurice in terms of both its position and its military power . Construction began in 1892 and the fort became operational in 1894 . The fort was nearly constantly upgraded with new artillery in increasingly secure positions . Following an incident in which three ammunition magazines exploded in close succession in 1946 , the fort was repaired and upgraded with two fully automatic 155mm gun turrets with a range of almost . After reassessments by the Swiss Armed Forces of their requirements for fixed fortifications , Dailly was progressively closed down starting in 1995 , with full closure at the end of 2003 . Fortress complex . The Fort de Dailly is the largest part of a fortress complex extending the length of the Saint - Maurice valley , with coordinated fields of artillery fire and interlocking defenses . While most of these positions are detached from one another and are self - sufficient installations , Dailly and its neighbor Savatan are connected . The Fort de Savatan adjoins Dailly at a lower level , facing to the north , and is connected by an inclined funicular in the mountain . The forts at Dailly and Savatan were completed in 1894 and became the central elements of Fortress Saint - Maurice . They were progressively expanded and upgraded through the twentieth century . Over time , Dailly was equipped with an example of virtually every Swiss artillery piece and construction method , from rock - cut artillery galleries to revolving gun turrets . The Fort de Dailly and surrounding installations were manned through their modern history by Fortress Brigade 10 . Dailly and Savatan comprised Fortress Group 2 , under Fortress Regiment 19 of Fortress Brigade 10 . Description . Fort de Dailly is one of the largest and most heavily armed forts in Switzerland , and the central position in Fortress Saint - Maurice . The artillery fort is located on the end of the Dailly massif at a higher level than Savatan , with fields of fire to the north , west and south . The fort therefore is capable of firing on an enemy advancing southeast into the heart of the Alpine redoubt from the direction of Lac Léman , or northwest from the Great Saint Bernard or Simplon passes . Work began at Dailly in 1892 . The entrance to the underground fort lies at an elevation of at the end of 29 switchbacks . The fort initially was armed with six 120mm gun turrets with additional open artillery positions . Two 75mm guns were mounted in casemates , while portable 53mm gun turrets occupied prepared surface positions . Dailly was upgraded with 105mm artillery during the 1940s , with as many as ten 105mm guns in casemate positions . Flanking coverage from across the valley was provided by the Fort du Scex . The construction of Dailly and other fortifications at Saint - Maurice raised concerns in France at the turn of the twentieth century . The Saint - Maurice defenses were first reconnoitered in December 1896 by a French Colonel Raymond , followed by Lieutenant Vignon in July , 1898 . . French citizens working on the fortification projects were interviewed by the French " gendarmerie " . In 1901 the French military attaché in Berne obtained pictures of Dailly from a Swiss officer . Construction . Initial studies were carried out for a fortification at Savatan in 1890 . It became clear that a position in the higher Dailly massif to the south would protect forces on the Savatan plateau and would complement a battery on the opposite side of the valley at Scex . A small hotel on the site of an old weather observation station on the Dailly massif was chosen for the barracks . Robert Weber was the architect in charge of the works . Initial work installed two 150mm mortars on Dailly at an altitude of about , which remained in place until the 1920s . A single 120mm howitzer in an armored turret was installed on the summit , remaining in place through the 1940s . For local defense , two 84mm guns were placed in concreted casemate s near an observation point in 1894 , called the Batterie de la Galerie de Morcles . Heavier artillery was initially installed in open positions . 155mm Krupp field guns were installed in open emplacements in 1894 , allowing fire in two directions . Battery C15 was placed on the ridge between Righi and the Aiguille , firing north and south . Battery C10 with two 105mm guns and the Batterie Aiguille with the same equipment were placed near the summit . The Batterie de l ' Observatoire , located above the Galerie des Mordes , was equipped with four 120mm guns . The Batterie Rossignol placed two 120mm pieces each facing north and south , while the Batterie de Plan 2 and the Batterie de Righi each mounted two 120mm pieces . These were replaced in 1923 by Model 1912 120mm howitzers with a higher rate of fire . As construction continued , rotating guns were installed to exploit the broad field of fire afforded by the heights . Four or six 120mm guns on mobile were installed on tracks in the Righi area . The guns were stored in garages in the rock , and were in service until the 1930s , forming batteries E1 , E2 and E3 . Two or four mobile guns were converted to fixed positions , replacing the C10 battery . Fixed turret guns were installed in the 1930s . The Model 1939 105mm gun was developed with an underground barbette , with the gun carriage in an armored turret and only the barrel exposed . Battery Panaux , with two turrets , was placed in service in 1940 , remaining in service until 1994 . Lighter guns were installed for local defense . From 1907 the Batterie Aiguille at the east end of the Aiguille crest covered the direction of Javerne with 75mm guns . Two more guns installed in an open position between Righi and the Aiguille in 1909 formed the Batterie Golèze , covering the area of Demècre . The exposed nature of this battery led to its replacement with a rock - protected position in the 1940s , remaining in service until all 75mm guns were withdrawn in the 1980s . Open heavy gun positions were judged to be relatively safe from opposing artillery fire , given their altitude above any potential opposing batteries , which would interfere with an optimal firing trajectory for an attacker . However , after the First World War , confidence in this approach lessened . The open positions were abandoned in the 1930s , replaced by artillery galleries under rock protection . At the Battery Rossignol , elevation , a gallery was excavated of sufficient size to allow towed artillery to be moved , with branching galleries on either side mounting Bofors 105mm guns with a range of in ten armored positions . Four guns , aimed to the north , constituted the Batteries des . Four more , aimed to the south , were the Batterie de Plex , and two aimed to the east were the Batterie de Rosseline . Ammunition explosion and renovation . Dailly was the scene of an ammunition explosion on 28 May 1946 , when about 5500 105mm shells , amounting to 449 tons , exploded in three separate magazines successively . The blast threw all four 105mm guns of the Batterie de Plex from their emplacements and damaged six more . The 120mm guns of the C10 battery were also damaged . Six construction workers were killed , part of a crew working on a funicular shaft linking Dailly to the upper part of Savatan . The explosion was attributed to decomposition of nitrocellulose propellant . Two similar explosions happened at Grisons in June 1946 and at Blausee - Mitholz in 1947 , without loss of life . The damage to Dailly resulted in a comprehensive modernization of the fort , with additions of 81mm and 120mm mortars , removal of obsolete weapons and the installation of two modern 155mm gun turrets . An underground caserne for 650 men was built at this time , with NBC protection . The four 105mm guns of the Batteries des and the two 105mm guns of the Batterie de Rosseline were repaired and upgraded , but the four guns of the south battery were never replaced , as their rock cover was judged to be insufficient . The new 155mm gun turrets were mounted on barbette s deep , with an individual rate of fire of 30 rounds per minute in bursts , or 15 rounds per minute sustained . Design began in 1949 , with the first test firings in 1960 . The range of these new guns approached , sufficient to reach Montreux , Sion or the Chamonix valley in France . Battery T1 ( for " turret " or " tourelle " ) was located at the old E3 mobile 120mm battery at an elevation of . Battery T2 was located at on the Rosseline heights near Battery Planaux . Both batteries were operational from 1962 to 1994 . Additional measures included the replacement of the summit batteries with two 81mm fortress mortars , entirely buried in the mountain ' s peak . A battery of twinned 120mm mortars was added in the 1960s . Both batteries remained in service until 1994 . These batteries covered the entire Savatan massif . The abandoned Batterie de Plex was replaced by the Batterie Dailly Nord , which remained operational until the end of 2003 . Deactivation and present status . Dailly was partially deactivated in 1995 and fully decommissioned at the end of 2003 . With the other Saint - Maurice fortifications , it has been designated as a candidate for preservation , but is not open to the public .