The Columbia-class submarine now under construction by GDEB, will be the most advanced SSBN in the world and the largest submarine ever built by the United States. The SSBN classification is the US Navy acronym for a Submarine armed with Ballistic missiles, that is Nuclear-powered. The SSBNs have a different primary function than SSN fast attack submarines, and need different design features as well. As part of America's Nuclear Triad, an SSBN’s mission is to keep its position a secret, while serving as a strategic ballistic missile platform. Compare that to an SSN’s mission of actively seeking out and engaging all enemy targets in a wide range of environments. One of the interesting design changes made to the Columbia-class, is the switch to an “X-Stern” configuration of rudder/planes, from the existing “cross-shape” design now seen on Ohio-class SSBNs and Virginia-class SSN boats. Why did the US Navy decide to move to an X-shaped stern control plane design?