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Ohio Replacement - Design

The Navy formalized key ship specifications for both the United States' Ohio Replacement and United Kingdom's Successor Programs in a document signed 31 August 2012 at the Washington Navy Yard. Rear Adm. Thomas J. Eccles, chief engineer and deputy commander Naval Systems Engineering Directorate, Naval Sea Systems Command (NAVSEA) and Capt. William J. Brougham, Ohio Replacement program manager signed the Ohio Replacement First Article Quad Pack Ship Specification document, marking a major construction milestone. "This document marks significant forward progress for both the U.S. and UK future strategic submarine deterrent programs," said Brougham. "It is a direct result of the engineering rigor and professionalism of government and industry partners on both shores of the Atlantic."

Ship specifications are critical for the design and construction of the common missile compartment, which will be used by both nations' replacement fleet ballistic missile submarine (SSBN) programs. Specifically, the First Article Quad Pack Ship Specification establishes a common design and technical requirements for the four missile tubes and associated equipment that comprise each quad pack.

SSBN-X Design Features:

• 40-year service-life expectancy (through 2080)
• Life-of-Ship nuclear fuel core (refueling of core unnecessary)
• 87-inch diameter launch tubes, resulting in a 42-foot beam (or slightly larger)
• 16 launch tubes (down from 24 on the Ohio-class ships)
• 18,750 tons submerged displacement (nearly the same as the Ohio-class ships)
• Technology that will remain state-of-the-art through its 40-year life

The National Defense Authorization Act (NDAA) for Fiscal Year 2012 (FY12) directed the Secretary of the Navy and the Commander of U.S. Strategic Command (USSTRATCOM) to jointly submit a report to the congressional defense committees comparing four different options for the OHIO Replacement (OR) fleet ballistic missile submarine (SSBN) program. The four SSBN options analyzed were:

1. 12 SSBNs with 16 missile tubes each
2. 10 SSBNs with 20 missile tubes each
3. 10 SSBNs with 16 missile tubes each
4. 8 SSBNs with 20 missile tubes each

A formal Analysis of Alternatives considered both a Virginia class submarine with an added missile compartment and Ohio class production restart to fulfill the SSBN mission.

An Ohio-based SSBN design would resume building the Ohio design cannot be done because there is no Ohio production line. It has long since been re-tooled and modernized to build state-of-the-art Virginia-class SSNs using computerized designs and modular, automated construction techniques. An Ohio-based SSBN would:

• Not provide the required quieting due to Ohio design constraints and use of a propeller instead of a propulsor (which is the standard for virtually all new submarines)
• Require 14 instead of 12 SSBNs by reverting to Ohio class operational availability standards (incidentally creating other issues with the New START treaty limits)
• Suffer from reduced reliability and costs associated with the obsolescence of legacy Ohio system components.

The end result would necessitate procuring more submarines (14) to provide the required at-sea presence and each of them would be less stealthy and less survivable against foreseeable 21st century threats.

An SSBN design based on a Virginia-class attack submarine with a large-diameter missile compartment was rejected due to a wide range of shortfalls. It would:

• Not meet survivability (stealth) requirements due to poor hull streamlining and lack of a drive train able to quietly propel a much larger ship
• Not meet at-sea availability requirements due to longer refit times (since equipment is packed more tightly within the hull, it requires more time to replace, repair and retest)
• Not meet availability requirements due to a longer mid-life overhaul (refueling needed)
• Require a larger number of submarines to meet the same operational requirement
• Reduce the deterrent value needed to protect the country (fewer missiles, warheads at-sea)
• Be more expensive than other alternatives due to extensive redesign of Virginia systems to work with the large missile compartment (for example, a taller sail, larger control surfaces and more robust support systems) The Navy would be spending more money (on more ships) to deliver less deterrence (reduced at-sea warhead presence) with less survivability (platforms that are less stealthy).

A Virginia-based SSBN design with a smaller missile would carry forward many of the shortfalls of a Virginia-based SSBN, and add to it a long list of new issues. Developing a new nuclear missile from scratch with an industrial base that last produced a new design more than 20 years ago would be challenging, costly and require extensive testing. The Navy deliberately decided to extend the life of the current missile to decouple and de-risk the complex (and costly) missile development program from the new replacement submarine program. Additionally, a smaller missile means a shorter employment range requiring longer SSBN patrol transits. This would compromise survivability, require more submarines at sea and ultimately weaken deterrence effectiveness. With significant cost, technical and schedule risks, there is little about this option that is attractive.

One of the key decisions that was made to drive the cost of that ship down was a decision to go from 20 missile tubes to 16 missile tubes, because that allowed designers to down rate the propulsion power that was needed, so obviously, a smaller reactor was need. This also allowed designers to go back to the use of existing components. The size of the boat fell into the envelope where designers could use components that had already been designed for the Virginia class attack submarines and bring those into this design, not have to do it over again.

The ORP will utilize Virginia-class�s fly-by-wire joystick control system and large-aperture bow array sonar. The ORP will also use Virginia-class�s next-generation communications system, antennas and mast. For instance, what used to be a periscope is now a camera mast connected to fiber-optic cable, enabling crew members in the submarine to see images without needing to stand beneath the periscope. This allows designers to move command and control areas to larger parts of the ship and still have access to images from the camera mast.

Many variations of stern control surfaces have been incorporated in the world's submarines over the years, including the traditional cruciform design and X-Stern. As of 2012 the Navy was considering a twin-rudder design, the H-Stern, for potential use on the Ohio Replacement. The H-Stern configuration offers potential for reducing disturbances to the propulsor inflow and could enable improved ship maneuverability using smaller�but more numerous�control surfaces and actuators.