public void set_nation(String nation){
		this.nation=nation;
		switch (this.nation){
			case "all":
				this.nation_nr=0;
				break;
			case "American":
				this.nation_nr=1;
				break;
			case "British":
				this.nation_nr=2;
				break;
			case "German":
				this.nation_nr=3;
				break;
			case "French":
				this.nation_nr=4;
				break;
			case "Soviet":
				this.nation_nr=5;
				break;
			case "Chinese":
				this.nation_nr=6;
				break;     
		}
	}