Ohio-class submarine
The "Ohio" class of nuclear-powered submarines includes the United States Navy's 14 ballistic missile submarines (SSBNs) and its four cruise missile submarines (SSGNs). Each displacing 18,750 tons submerged, the "Ohio"-class boats are the largest submarines ever built for the U.S. Navy. They are the world's third-largest submarines, behind the Russian Navy's Soviet-designed 48,000-ton and 24,000-ton . The "Ohios" carry more missiles than either: 24 Trident II missiles apiece, versus 16 by the Borei class (20 by the Borei II) and 20 by the "Typhoon" class. Like its predecessor - and subs , the "Ohio" SSBNs are part of the United States' nuclear-deterrent triad, along with U.S. Air Force strategic bombers and intercontinental ballistic missiles. The 14 SSBNs together carry about half of U.S. active strategic thermonuclear warheads. Although the Trident missiles have no preset targets when the submarines go on patrol, they can be given targets quickly, from the United States Strategic Command based in Nebraska, using secure and constant radio communications links, including very low frequency systems. The lead submarine of this class is . All the "Ohio"-class submarines, except for , are named for U.S. states, which U.S. Navy tradition had  previously reserved for battleships and cruisers. The "Ohio" class is to be gradually replaced by the beginning in 2031. Description. The "Ohio"-class submarine was designed for extended strategic deterrent patrols. Each submarine is assigned two complete crews, called the Blue crew and the Gold crew, each typically serving 70-to-90-day deterrent patrols. To decrease the time in port for crew turnover and replenishment, three large logistics hatches have been installed to provide large-diameter resupply and repair access. These hatches allow rapid transfer of supply pallets, equipment replacement modules, and machinery components, speeding up replenishment and maintenance of the  submarines. Moreover, the "stealth" ability of the submarines was significantly improved over all previous ballistic-missile subs. " Ohio" was virtually undetectable in her sea trials in 1982, giving the U.S. Navy extremely advanced flexibility. The class's design allows the boat to operate for about 15 years between major overhauls. These submarines are reported to be as quiet at their cruising speed of or more as the previous s at , although exact information remains classified. Fire control for their Mark 48 torpedoes is carried out by Mark 118 Mod 2 system, while the Missile Fire Control system is a Mark  98. The "Ohio"-class submarines were constructed from sections of hull, with each four-deck section being in diameter. The sections were produced at the General Dynamics Electric Boat facility, Quonset Point, Rhode Island, and then assembled at its shipyard at Groton, Connecticut. The US Navy has a total of 18 "Ohio"-class submarines which consist of 14 ballistic missile submarines (SSBNs), and four cruise missile submarines (SSGNs). The SSBN submarines provide the sea-based leg of the U.S. nuclear triad. Each SSBN submarine is armed with up to 24 Trident II submarine-launched ballistic missiles (SLBM). Each SSGN is capable of  carrying 154 Tomahawk cruise missiles, plus a complement of Harpoon missiles to be fired through their torpedo tubes. As part of the New START treaty, four tubes on each SSBN will be deactivated, leaving each ship with only 20 available for war loads. History. The "Ohio" class was designed in the 1970s to carry the concurrently designed Trident submarine-launched ballistic missile. The first eight "Ohio"-class submarines were armed at first with 24 Trident I C4 SLBMs. Beginning with the ninth Trident submarine, , the remaining boats were equipped with the larger, three-stage Trident II D5 missile. The Trident I  missile carries eight multiple independently targetable reentry vehicles, while the Trident II missile carries 12, in total delivering more destructive power than the Trident I missile and with greater accuracy. Starting with in 2000, the Navy began converting its remaining ballistic missile submarines armed with C4 missiles to carry D5 missiles. This task was completed in mid-2008. The first eight submarines had their home ports at Bangor, Washington, to replace the submarines carrying Polaris A3 missiles that were then being decommissioned. The remaining 10 submarines originally had their home ports at Kings Bay, Georgia, replacing the Poseidon and Trident Backfit  submarines of the Atlantic Fleet. SSBN/SSGN conversions. In 1994, the Nuclear Posture Review study determined that, of the 18 "Ohio" SSBNs the U.S. Navy would be operating in total, 14 would be sufficient for the strategic needs of the U.S. The decision was made to convert four "Ohio"-class boats into SSGNs capable of conducting conventional land attack and special operations. As a result, the four oldest boats of the class—"Ohio", "Michigan", "Florida", and "Georgia"—progressively entered the conversion process in late 2002 and were returned to active service by 2008. The boats could thereafter carry 154 Tomahawk cruise missiles and  66 special operations personnel, among other capabilities and upgrades. The cost to refit the four boats was around US$1 billion (2008 dollars) per vessel. During the conversion of the first four submarines to SSGNs (see below), five of the submarines, , , , , and , were transferred from Kings Bay to Bangor. Further transfers occur as the strategic weapons goals of the United States change. In 2011, "Ohio"-class submarines carried out 28 deterrent patrols. Each patrol lasts around 70 days. Four boats are on station ("hard alert") in designated patrol areas at any given time. From January to June 2014, "Pennsylvania" carried out  a 140-day-long patrol, the longest to date. The conversion modified 22 of the 24 diameter Trident missile tubes to contain large vertical launch systems, one configuration of which may be a cluster of seven Tomahawk cruise missiles. In this configuration, the number of cruise missiles carried could be a maximum of 154, the equivalent of what is typically deployed in a surface battle group. Other payload possibilities include new generations of supersonic and hypersonic cruise missiles, and Submarine Launched Intermediate Range Ballistic Missiles, unmanned aerial vehicles, the ADM-160 MALD, sensors for antisubmarine warfare or intelligence, surveillance, and reconnaissance  missions, counter mine warfare payloads such as the AN/BLQ-11 Long Term Mine Reconnaissance System, and the broaching universal buoyant launcher and stealthy affordable capsule system specialized payload canisters. The missile tubes also have room for stowage canisters that can extend the forward deployment time for special forces. The other two Trident tubes are converted to swimmer lockout chambers. For special operations, the Advanced SEAL Delivery System and the dry deck shelter can be mounted on the lockout chamber and the boat will be able to host up to 66 special-operations sailors or Marines, such as Navy SEALs, or  USMC MARSOC teams. Improved communications equipment installed during the upgrade allows the SSGNs to serve as a forward-deployed, clandestine Small Combatant Joint Command Center. On 26 September 2002, the Navy awarded General Dynamics Electric Boat a US$442.9 million contract to begin the first phase of the SSGN submarine conversion program. Those funds covered only the initial phase of conversion for the first two boats on the schedule. Advanced procurement was funded at $355 million in fiscal year 2002, $825 million in the FY 2003 budget and, through the five-year defense budget plan, at $936  million in FY 2004, $505 million in FY 2005, and $170 million in FY 2006. Thus, the total cost to refit the four boats is just under $700 million per vessel. In November 2002, "Ohio" entered a dry-dock, beginning her 36-month refueling and missile-conversion overhaul. Electric Boat announced on 9 January 2006 that the conversion had been completed. The converted "Ohio" rejoined the fleet in February 2006, followed by "Florida" in April 2006. The converted "Michigan" was delivered in November 2006. The converted "Ohio" went to sea for the first time in October 2007 . "Georgia" returned to the fleet in March 2008 at Kings Bay. These four SSGNs are expected to remain in service until about 2023–2026. At that point, their capabilities will be replaced with Virginia Payload Module-equipped . List of boats. Note: Boats based at Naval Base Kitsap, Washington are operated by the U.S. Pacific Fleet, while boats based at Naval Submarine Base Kings Bay, Georgia are operated by U.S. Fleet Forces Command, (formerly the U.S. Atlantic Fleet). Replacement. The U.S. Department of Defense anticipates a continued need for a sea-based strategic nuclear force. The first of the current "Ohio" SSBNs  is expected to be retired by 2029, so the replacement submarine must be seaworthy by that time. A replacement may cost over $4 billion per unit compared to "Ohio"s $2 billion. The U.S. Navy is exploring two options. The first option is a variant of the nuclear-powered attack submarines. The second option is a dedicated SSBN, either with a new hull or based on an overhaul of the current "Ohio". With the cooperation of both Electric Boat and Newport News Shipbuilding, in 2007, the U.S. Navy began a cost-control study. Then in December 2008, the U.S.  Navy awarded Electric Boat a contract for the missile compartment design of the "Ohio"-class replacement, worth up to $592 million. Newport News is expected to receive close to 4% of that project. In April 2009, U.S. Defense Secretary Robert M. Gates stated that the U.S. Navy was expected to begin such a program in 2010. The new vessel was scheduled to enter the design phase by 2014. If a new hull design was to be used, the program needed to be initiated by 2016 to meet the 2029 deadline. The "Columbia"-class was officially designated on 14 December 2016, by  Secretary of the Navy Ray Mabus, and the lead submarine will be . The Navy wants to procure the first Columbia-class boat in FY2021, though it's not expected to enter service until 2031. In popular culture. As ballistic-missile submarines, the "Ohio" class has occasionally been portrayed in fiction books and films.