4, 50 Fr. Postal stamp with overprint \"fortress Lorient\" as a single franking (overfranked) on cover from the \"fortress Lorient 20. April 1945\" to La Baule with reverse arrival stamp from 30.4 45, the letter was poste restante mailed and at destination \"La Baule\" was the post storage fee of 1 Fr. Later calculated and with the red machine cancel receipted, without any signature and photo expertize Lothar Herbst VP (2015) : \"the condition is perfect. A nice cover. The stamp has only a very small edition from 100 pieces. Covers of the fortress post Lorient are general very rare. So far are from of this stamp only 4 covers registered, the all over franked single frankings are and in the fortress St. Nazaire used are. Therefore an extreme rare cover. \" Michel 6.500.-