DD-21

SC-21 (Surface Combatant for the 21st century) was a research and development program started in 1994 intended to design land attack ships for the United States Navy. A wide variety of designs were created and extensively examined, including an arsenal ship with 500 cruise missiles. Eventually a "tumblehome" design of around 16,000 tons with two long-range guns and 128 missile tubes was selected as the DD-21, the Destroyer for the 21st century. The program ended in November 2001, with a version of the DD-21 emerging as the DD(X) or Zumwalt class destroyer. It was envisaged that the DD-21 hull would be used for a future air defense cruiser (CG-21), which then eventually evolved into the CG(X) program.

The origins of SC-21 lie in the realization by Admiral Joseph Metcalf III that new technologies such as vertical launch missiles permitted a complete rethink of warship design. He established a steering group, Group Mike, to study the possibilities. Group Mike sponsored two studies in 1987, the Ship Operational Characteristics Study (SOCS) and the Surface Combatant Force Requirement Study (SCFRS). SOCS sought to identify the operational characteristics required of an escort ship, and SCFRS estimated how many such ships were required by the fleet. Since it was expected at that time that the Navy would be fighting prolonged campaigns in the Norwegian Sea, SOCS put an emphasis on ships' continuing ability to fight after an initial Soviet attack. This in turn called for larger, more survivable escort ships than had historically been the norm, around 12,000 tons, and for networking sensors and weapons together so that they could be used by the task force as a whole even if an individual ship had their radar disabled. Survivability also called for the bridge and Combat Information Center to be combined and "buried" in the heart of the ship, and for the ship to use electric drive to distribute the engineering around the ship, which would also give more room for weapons and the scope for railguns and laser weapons in future. SCFRS suggested that the Navy should not replace the Perry class frigate for convoy escort duties, but concentrate on building front-line combatants that could be assigned to less demanding convoy duties in their later years.

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