The machine gun was the principal weapon of the Maginot Line. Every casemate had several of them for flanking fire and the close in defense. The drawing shows the so-called Jumelage de Mitrailleuses, a heavy twin MG in calibre 7,5 mm. This configuration was choosen, because the two weapons could alternate their fire, while was cooling. In case of a massive attack both weapons could fire at the same time. The machine guns were fed by a large round magazine holding 150 rounds. For more information click here.