Many techniques and mechanisms exist today, some COTS, others less mature research products that can be used to deflect, detect, or even recover from specific types of cyber attacks. None of them individually is sufficient to provide an all around defense for a mission critical distributed system. A mission critical system must operate despite sustained attacks throughout the mission cycle, which in the case of military systems, can range from hours to days. A comprehensive survivability architecture, where individual security tools and defense mechanisms are used as building blocks, is required to achieve this level of survivability. We have recently designed a survivability architecture, which combined elements of protection, detection, and adaptive reaction; and applied it to a DoD information system. The resulting defense-enabled system was first evaluated internally, and then deployed for external Red Team exercise. In this paper we describe the survivability architecture of the system, and explain the rationale that motivated the design.