2 Fr. dark bluish green with overprint "fortress Lorient" with right attaching and also overprinted note empty space being a correctly franked single franking on cover from "Lorient 10 April 1945" to tepid Baule in the fortress St. Nazaire with arrival postmark 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 autumn VP (2015) : "the condition is perfect. The stamps have only a very small issue from 150 piece, so that they very rare are. Stamps with empty space are only approximate 15 pieces possible and are therefore extremely rare. Covers of the fortress post Lorient are general very rare. "