A lighthouse, particularly one that is offshore, cannot operate without a logistical supply chain to provide fuel and other materials. Since the 1730s, Cordouan was linked to Royan, where a house had been purchased to store coal, which was brought to the lighthouse by launch. During the nineteenth century, the Lighthouse Service extended its mandate to include markers, i.e. every device that helped sailors to navigate both day and night: buoys, towers, daymarks and spars. In particular, the goal was to improve the channel markings in the major estuaries. Iron buoys were constructed, whose upkeep required new maintenance and storage zones – marker depots – as well as a specific fleet of tenders for laying and retrieving them. The Cordouan house at Royan was transformed into a marker depot and became the home port for the Éclaireur de la Gironde. In the 1890s, a plant was built for producing the gas required for the 38 lighted buoys that marked the estuary all the way to Bordeaux. At the end of the 1920s, a major project was launched to turn Verdon-sur-Mer into an "outer port of call" for Bordeaux. It was decided to transfer the marker depot, financed by the Port Autonome, which had a large budget due to the sale of the depot's land on Rue de la Marine. In addition to workshops, housing was built for the engineer, the Cordouan keepers and their families. The "industrial" connection between Royan and Cordouan was severed for the benefit of the left shore.