section. The state granted the national railway a loan of 35 million Reichsmarks (equivalent to €145m). Work on this began as early as 1928, but it was not until 1941 that the work was largely complete, apart from a 2.3-kilometre section between Aistaig and Oberndorf am Neckar. This last section followed in 1943. A simplification of operations had been enabled by the commissioning of the Tuttlingen–Hattingen railway in 1933. It removed the need for trains to and from Singen to detour via Immendingen and reverse there. In the course of the upgrade at that time, Deutsche Reichsbahn also greatly expanded Horb and Rottweil stations and replaced Tuttlingen station with a large new building. During the Second World War, the Mauser works in Oberndorf am Neckar, an important pillar of German arms production, was an important business on the line. During the war, the line was largely spared from major destruction until February 1945. In 1944/45, Allied aerial bombing caused serious damage to the stations in Horb, Rottweil, Spaichingen and Tuttlingen, but these did not interrupt traffic permanently. It was not until February 1945 that Allied bomber formations destroyed a bridge during an attack on Oberndorf, disrupting rail traffic. After the war, France, unlike the United States, exercised its right to reparations on a large scale and in 1946 dismantled the second track between Horb and Tuttlingen that had been laid only a few years earlier. On 25 September 1977, the Horb–Tuttlingen section was electrified. At the same time, Deutsche Bundesbahn abandoned services at numerous stations on this section in order to increase travel speeds in local traffic through so-called "express train driving". During the electrification, the iron girder bridge on the disused Balingen–Rottweil line had to be removed to make room for the catenary. Also due to the resticted loading gauge, the remaining track in the five tunnels of this section has been running in the middle since then, which makes it difficult to restore double track. The former stations at , Betzingen and Kirchentellinsfurt were downgraded halts in the second half of the 20th century. In addition, practically all sidings between Plochingen and Tübingen, many sidings and freight yards were abandoned and mostly separated from the main-line track during conversions. In the course of the introduction of the Ringzug ("ring train"), which serves the route between Rottweil and Immendingen, in 2003, DB Station&Service reactivated several abandoned stations and built