Although metal caissons were originally planned to be sunk vertically (as had been done on Line 4), a tunnel was drilled following a single circular tube with the aid of a shield; authorities opposed the first method because of the risks to boating. However, the crossing near Pont Mirabeau was made with vertical caissons. The Invalides-Javel section was completed in 1910. The Grenelle station was planned as a double station with platforms on two levels, with the aim to later send trains on the two branches. However, only one station with a central platform was built, as the Balard branch was planned to be built later.