Offshore lighthouses are a remarkable historical heritage often over 100 years old. The management of their aging is a challenge. The extremely low permeability of Ultra-High- Performance Fiber Reinforced Concretes (UHPFRC), combined with their outstanding mechanical properties (robust tensile Strain Hardening (SH) for specific mixes) are particularly suitable for the reinforcement of this type of structures and more generally offshore maritime signalization structures. These structures under the influence of tides and weather, exposed to a very aggressive environment, have very limited access. As for existing bridges, SH-UHPFRC provide in this case a robust, effective, and very durable reinforcement solution, making it possible to simplify and reduce the duration of interventions. In this context, an existing turret at sea, on the south coast of Brittany, was reinforced by the application of a 60 mm UHPFRC hull, cast in place by helicopter in a formwork around the existing masonry structure. This application paves the way for the reinforcement with the same materials of lighthouses at sea exposed to extreme weathering conditions, such as "La Jument" nearby the island of Ushant (Brittany, France).