2 Fr. postal stamp with inverted overprint "fortress Lorient" as correctly franked single franking on cover to La Baule in the fortress St. Nazaire, between the both German Atlantic fortresses inventory a local established postal service traffic by sea during the period between January and May 1945, signed Romuet and photo expertize Lothar autumn VP (2015) : "the condition is perfect. The stamp has only a very small printing from 150 piece, so they are very rare, especially inverted overprints. Covers of the fortress post Lorient are general very rare. "