This issue paper presents a concept for improving both how the US military assembles forces for integrated joint operations in an uncertain security environment and how it transforms forces to exploit technology and meet long-term needs. Joint operations integrated by common information networks are key to enabling the United States to overcome a wide and fluid assortment of threats and meet its global security needs. The author suggests a new architecture for preparing and assembling forces: At its center is a battle-management nucleus combined with certain joint core capabilities that would be kept in place at all times within each regional combatant command. In crises, this small but critical standing capability would be augmented by building blocks of main forces--Army brigades, Navy carrier and expeditionary strike groups, Marine expeditionary units, Air Force expeditionary forces, and the like--that are prepared by the individual services to fit into and fight as an integrated force. Exercising the nucleus, the nucleus plus core, and the nucleus plus core plus building blocks in various combinations would be a major peacetime readiness responsibility of the joint combatant commands. This architecture would help ensure fast and flexible transition from peacetime to contingency operations. The same architecture also suggests a workable division of responsibilities for transformation between the services and the joint community.