The supply of the Isonzo battlefield depended on road and rail traffic. Road traffic was radically reduced due to the lack of horses and cars, so the construction of narrow-gauge railways was accelerated. One of these was the 80 kilometres long horse-drawn field railway (Feldbahn) Dolenji Logatec–Kalce–Godovič–Črni Vrh–Zadlog–Poncala (Mala Lazna). Its construction began on 15 August 1916 and the transportation from Logatec to Zadlog began on 9 September, during the Seventh Isonzo Offensive. The continuation of the narrow-gauge railway from Zadlog to Mala Lazna (Poncala) was opened for traffic on 29 November 1916.
When the Italian Army severly damaged the Bohinj standard tracks during the Sixth Isonzo Battle in August 1916, the trains from the direction of Jesenice could only go to Grahovo in Baška grapa, so the command was forced to look for new connections to secure uninterrupted supply of the front. The decision was taken that the main starting point for supply would be the Logatec railway station. Since after the Ninth Isonzo Offensive in 1916 the Austro-Hungarian Army had to withdraw to higher positions towards Čepovan and the Trnovska Planota plateau, the supreme military command which had its headquarters at Gorenji Logatec demanded immediate construction of a standard track line from Logatec to Črni Vrh.
Works began immediately after the approval of the plan, where the construction of tunnels, major excavations and embankments on the approved route had priority. Though field measurements were carried out in military secrecy, the plan soon became evident.
The drilling of tunnels in Logatec and Godovič took precedence over everything else.
According to the veterans, as many as 20,000 prisoners of various nationalities were deployed along the route. They were located in the camps of Dolenji Logatec, Kalce, Hotedršica and in Gorenji Logatec Castle.
The line was divided into three sectors with the total length of 25 kilometres:
The Logatec–Kalce section was the most demanding, mainly due to the connection to the Vienna–Trieste railway line. The problem was solved with a large embankment, which descended in a wide curve from the higher lying Southern Railway to Logaško polje, and from there through the tunnel under Naklo and past Lokva towards Kalce. By the Logatec–Vrhnika road, the construction of a shunting station and a turning point for locomotives began.
The most demanding task was the construction of a 202 metres long tunnel under Naklo. The construction of the tunnel was taken over by the Redlich-Berger company of Graz, the one that also constructed the Solkan stone bridge. Works began in the spring of 1917. Water impeded the work, so a special drainage system was made and the water was smartly directed via the central installation channel to a natural abyss, about 20 metres before the end of the tunnel on the east side. By tilting the ground, the constructors ensured that water drained in a natural way.
While digging the tunnel, the workers came across a seam of bituminous coal, which was used partly for fuelling the locomotive that transported away the excavated material, and partly for heating locals’ homes.
The narrow-gauge railway was used for transporting away the material of tunnel excavation. A steam locomotive, affectionally named by workers “Mašinka”, was used for pulling the train. The tunnel was completed early in 1917.
In the spring of the same year, all the works on the railway embankments in the area of the Logatec basin were mainly completed, and in many places the laying of sleepers for the rails began. Concurrently, intensive works began on the tunnel at Kalce.
The shift of the front to the Piave River in northern Italy meant that the Logatec–Črni Vrh transport line no longer met the strategic needs of the army, consequently all subsequent works were stopped. Except for Mašinka with the excavation material, no train ever passed through the tunnel. The quality of tunnel construction makes it solidly preserved even today.
During World War II, the tunnel served as a shelter for the people of Logatec. Built for this purpose were partition walls, which also prevented stronger draughts. Supposedly, it was also a fuel depot.
The Municipality of Logatec is making the tunnel ready for use by pedestrians and cyclists as a connection between Naklo and the Logatec Administrative Centre. In the autumn of 2020, a life-size replica of the “Mašinka” was placed in the park which lies 120 metres away from the west entrance to the tunnel. Since such locomotives were mainly made for tunnel constructions, they are rather small compared to the freight locomotives.
From Tržaška street, at the crossroads at Petrol’s gas station, turn towards the Logatec Administrative Centre and park at the parking lot to its right. On the NE side of the parking lot, at the transformer station, turn right to the path by which a replica of the locomotive can already be seen.