On Armor tells three important and interconnected stories. The first is a tale of a technology, in particular, the rise and fall of the main battle tank--a type of armored vehicle that came to dominate land warfare in the middle of the 20th century but is now obsolete. The second is a history of ideas. The problem that armored vehicles created for 20th-century armies was as much about concepts of operation as it was about technology. Those who got the philosophy right did well. Those who lacked either the imagination or the intellectual capital to understand the rapidly evolving potential of the armored vehicle failed miserably. The third story is one of organization. Gudmundsson pays particular attention to how armored vehicles were combined with other forces to form an extraordinarily rich variety of units and formations. He also comments on the current and future roles various types of armor will play on the battlefield.