It was centred around the port and the submarine base of Saint-Nazaire and extended to the east as far as Saint-Omer-de-Blain and from La Roche-Bernard in the north to Pornic in the south. The Germans wanted to retain these strategic areas and declared them "fortresses" German : Festung.
Also denying the Allies these deep-water ports would hamper operations following the Normandy campaign. The Allies also favoured a mainly eastward advance of the offensive towards Germany. The Brest pocket fell on 18 September after hard fighting, the other four lasted until the surrender of the 8 May , or shortly thereafter. This particular pocket centered on the town and fortified submarine base of Saint-Nazaire but spread out further.
North of the Loire , the front line followed the left bank of the Vilaine river, then the Isac the Nantes-Brest canal , as far as the part of Blain west of the canal; it then descended south-west to Cordemais , passing between Bouvron , Fay-de-Bretagne and Le Temple-de-Bretagne. The coastal defensive sector of the pocket stretched over approximately 50 kilometres 31 miles of coastline. In total, the Germans had guns of all kinds fixed, mobile and anti-aircraft , with a higher density around the submarine base, the port facilities and the airfield.
Closer to Saint-Nazaire, there was a belt of anti-tank ditches. South of the Loire, the belt described a circle from Paimboeuf to the south of Saint-Brevin. Altogether it is estimated that this pocket fortress had 28, German soldiers commanded by Aviation General Hans Junck [ de ]. The submarine base remained under the command of Admiral Hans Mirow [ de ]. The pocket also contained nearly , civilians. By October , a large number of them women and children were allowed to leave the pocket, easing pressure on the Germans to feed them.
Other convoys were subsequently organized by the Red Cross. Trains left the pocket near Cordemais. A temporary truce was observed between the belligerents during their journey. Other inhabitants left the pocket by their own means, in particular on its eastern and southern limits: for example, some of the inhabitants of Fession Saint-Omer-de-Blain left their farms, under constant American mortar fire at the end of November , and went east through the mined lines.
