Gerhardt City is, despite the German name, an Italian city. This city was attacked by the Rebel Army during the First Modern War. Mission 5 -The City Under Despotism- takes place here, and the 2nd mission of Metal Slug 4 takes place here as well, though in the latter the mission continues through Ridge 256. Although its location is vague, it's probabily inspired to the city of Trieste, sharing with it some characteristics: Trieste, although Italian, has a German-speaking minority, is a coastal city but surrounded by mountains (the Alps) and has a very busy haven, as you can see Gerhardt City (2nd mission of Metal Slug 4).