The doctrine of armored warfare changed radically in the inter-war years as armies sought ways to avoid the deadlock imposed by modern firepower and looked for the means to restore offensive power on the battlefield. Initially, tanks had been used for close support of infantry, but as modern mechanized doctrine was developed by several armies, tanks became an essential part of the combined-arms team. In addition to infantry support, tanks fulfilled traditional cavalry roles, provided mobile artillery support, and were adapted to combat engineering roles.