2 Fr. Postal stamp with inverted overprint \"fortress Lorient\" as properly 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, expertized Roumet and photo expertize Lothar Herbst VP (2015) : \"the condition is perfect. The stamp has only a very small edition from 150 piece, so they are very rare, especially inverted overprints. Covers of the fortress post Lorient are general very rare. \" Michel 2.800.-