From Wiktionary, the free dictionary
From ships that sank with man and mouse, i.e. bringing about the death of every living thing on them. The expression was then generalized in German.
mit Mann und Maus
- (somewhat informal) to a man, with everybody, with all means available
Die Stadtbewohner verteidigten sich mit Mann und Maus.- The town dwellers defended themselves to a man.
