The U.S. Army plans to spend about an additional $34 billion in 2013 dollars to develop and purchase a new armored vehicle for its infantry, the Ground Combat Vehicle (GCV). The GCV is supposed to operate across the full range of potential conflict types while providing unprecedented levels of protection for the full squad of soldiers it will carry. To achieve the Army's goals, the GCV would weigh from 64 to 84 tons, making it the biggest and heaviest infantry fighting vehicle that the Army has ever fielded-as big as the M1 Abrams tank and twice as heavy as the Bradley, the Army's current infantry fighting vehicle. Designing such a vehicle presents important technical challenges. To aid the Congress in its oversight of the GCV program, the Congressional Budget Office (CBO) has prepared two reports. This CBO working paper provides background information for understanding the technical challenges that the program faces. It presents the Army's technical goals for the GCV program, examines the threats that the vehicle could face in combat, and explores the variety of approaches that vehicle designers can take to protect the vehicle and its passengers and to meet the Army's other requirements. A companion report, The Army's Ground Combat Vehicle Program and Alternatives, examines the GCV program (including the number of vehicles, the production schedule, and the cost) and alternative approaches that the Army could take that would cost less but still provide substantial improvements over today's fleet of combat vehicles.