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 - an armoured vehicle that came to dominate land warfare in the middle of the 20th century. The second is a history of ideas. The problem that armoured vehicles created for 20th-century armies was as much about concepts of operation as it was about technology. The third story is one of organization. The author pays particular attention to how armoured vehicles were combined with other forces to form a rich variety of units and formations. He also comments on the current and future roles various types of armour will play on the battlefield.