Reconstruction started in 1945. Trains first returned to the facilities above ground. By the end of May and early June 1945 the BVG, the operator of Berlin's U-Bahn, had sealed up the pedestrian tunnel between tunnel S-Bahn and U-Bahn station to stop water flooding into the tunnel. Reichsbahn, the operator of the S-Bahn, had declared that it lacked the means to close the tunnel leaks. On 4 June BVG started the drainage of its underground system. On 12 July the underground reopened its Friedrichstraße station for two one-track shuttle operations, one from north and one from south meeting there, regular two-track traffic restarted on since 5 December 1945. Reichsbahn drained its North-South tunnel only later and reopened below-ground S-Bahn service on 2 June 1946. On 1 December the same year North-South tunnel and Friedrichstraße below-ground S-Bahn station shut again for an extensive refurbishment which lasted until 16 October 1947, when the North-South tunnel was fully operational again.