2 Fr. Dark bluish green with overprint \"fortress Lorient\" with right attaching and also overprinted note blank field as properly franked single franking on letter from \"Lorient 10 April 1945\" to tepid Baule in the fortress St. Nazaire with arrival stamp from 20.4.45, between the both German Atlantic fortresses inventory from January - May 1945 a local established postal service traffic over the sea route, faultless condition, photo expertize Lothar Herbst VP (2015) : \"the condition is perfect. The stamps have only a very small edition from 150 piece, so they are very rare. Stamps with blank field are only approximate 15 pieces possible and are therefore extremely rare. Covers of the fortress post Lorient are general very rare. \"