Kidou Senshi Gundam: Acguy Hokubei Oudan 2250 Miles

This story takes place during December 0079 U.C. where two brothers are forced to traverse the North American territory as the rear guard of the retreating Principality of Zeon forces, using MSM-04 Acguy amphibious mobile suits, after the Principality fails to capture the Earth Federation's headquarters at Jaburo. However it doesn't take long before these two brothers are the only ones left alive and are faced with the prospect of travelling over two thousand miles, without supplies and backup.