General Dynamics Ohio-class SSGN

History

The General Dynamics Ohio-class guided-missile submarine, designated SSGN, is a converted nuclear-powered submarine operated by the United States Navy. Four early Ohio-class ballistic-missile submarines were rebuilt as conventional strike and special-operations platforms.

Each converted submarine can carry up to 154 Tomahawk land-attack cruise missiles. It can also transport special operations forces, deploy them through underwater lock-out chambers, support uncrewed systems, and operate as a concealed command and intelligence platform.

The four SSGNs are USS Ohio, USS Michigan, USS Florida, and USS Georgia. Their combination of a large payload, nuclear endurance, enhanced communications, and two alternating crews made them important long-duration power-projection platforms.

Conversion program

The original Ohio class was developed as a fleet of 18 ballistic-missile submarines. USS Ohio, the lead boat, was launched in 1979 and commissioned in 1981. The first four boats initially carried Trident I submarine-launched ballistic missiles.

The 1994 Nuclear Posture Review concluded that the United States required 14 rather than 18 Ohio-class ballistic-missile submarines for strategic deterrence. The Navy consequently selected Ohio, Michigan, Florida, and Georgia for conversion into conventionally armed SSGNs instead of retiring them.

The conversion program began with USS Ohio entering a shipyard in November 2002. General Dynamics Electric Boat performed conversion work in cooperation with naval shipyards, while each submarine also received an Engineered Refueling Overhaul. Ohio completed conversion in December 2005, Florida returned to the fleet in April 2006, Michigan was delivered in November 2006, and Georgia completed conversion in December 2007. The U.S. Navy fact file provides the official program history and characteristics.

Design

Hull and internal arrangement

The SSGN retained the basic Ohio-class pressure hull, nuclear propulsion system, and single-shaft arrangement. The submarine is divided into forward, missile, reactor, and engine compartments. Its sail contains diving planes and housings for masts, antennas, and other equipment.

The original design had 24 large missile tubes behind the sail. During conversion, 22 tubes were adapted for conventional payloads. The two forward tubes became lock-out chambers through which special operations personnel can enter or leave the submarine while submerged.

Strike system

Each of the 22 strike tubes can accept a seven-missile Multiple-All-Up-Round Canister. This arrangement provides a theoretical maximum load of 154 Tomahawk land-attack cruise missiles. Operational loads can be smaller because tubes may instead carry equipment, supplies, or other mission payloads.

The large tubes were also designed to accommodate future payload types, including unmanned aerial and underwater vehicles. Four bow-mounted 533 mm torpedo tubes provide additional armament with Mk 48 torpedoes.

Special operations and command facilities

An Ohio-class SSGN can accommodate up to 66 special operations personnel. Additional berthing and storage were installed in the former missile compartment. Each lock-out chamber can support a Dry Deck Shelter for deploying and recovering personnel or swimmer-delivery vehicles underwater.

The conversion added a Common Submarine Radio Room and two high-data-rate antennas. These systems allow the submarine to exchange information and function as a concealed forward command center. The boats can also support intelligence collection and data fusion.

Propulsion and crew system

The submarine uses one nuclear reactor driving steam turbines and one propeller shaft. Nuclear propulsion permits extended submerged operations, with endurance principally limited by supplies and personnel requirements rather than propulsion fuel.

Each SSGN has separate Blue and Gold crews. The crews alternate responsibility for deployments, training, and maintenance, increasing the time that the submarine can remain operationally available.

Operational history

The four converted submarines conducted conventional strike, special-operations support, surveillance, and command missions. Their large Tomahawk capacity allowed one boat to deliver a substantial land-attack salvo while remaining concealed.

USS Florida demonstrated this role during Operation Odyssey Dawn in 2011. It launched more than 90 Tomahawk missiles against targets in Libya, marking the first combat launch of Tomahawks by a guided-missile submarine.

USS Georgia was repeatedly deployed to areas of geopolitical tension. It made publicized surface transits through the Strait of Hormuz in late 2020 and early 2021. During a May 2021 transit, Iranian boats approached Georgia and its escorts, after which a United States Coast Guard patrol boat fired warning shots.

Georgia returned to Naval Submarine Base Kings Bay on July 27, 2026, after its final operational deployment. A subsequent Navy update stated that the submarine would remain at Kings Bay until changing homeport to Norfolk for inactivation at Norfolk Naval Shipyard in July 2027.

The retirement schedule also called for Ohio, Florida, and Michigan to leave active service in fiscal years 2027, 2028, and 2029 respectively. These dates represented an extension of the earlier plan to retire all four boats by 2028.

Boats

• USS Ohio (SSGN 726): Lead boat of the Ohio class. It entered conversion in November 2002, completed the work in December 2005, and deployed in its new role in October 2007.
• USS Michigan (SSGN 727): Entered its conversion availability in October 2004 and was delivered as an SSGN in November 2006.
• USS Florida (SSGN 728): Began refueling and conversion in August 2003 and returned to the fleet in April 2006.
• USS Georgia (SSGN 729): The last of the four conversions. It completed conversion in December 2007 and returned to the fleet in its new configuration in 2008.

Operators

• United States: The United States Navy operated all four Ohio-class SSGNs for conventional strike, special-operations support, intelligence, and command missions.

Specifications (Ohio-class SSGN)

General characteristics

• Builder: General Dynamics Electric Boat Division
• Type: Nuclear-powered guided-missile submarine
• Length: 170.69 m (560 ft)
• Beam: 12.8 m (42 ft)
• Displacement: 17,033 metric tonnes surfaced; 19,000 metric tonnes submerged
• Crews: Two alternating Blue and Gold crews
• Personnel per crew: 15 officers and 144 enlisted personnel
• Special operations capacity: Up to 66 personnel

Performance

• Propulsion: One nuclear reactor driving one shaft
• Submerged speed: More than 20 knots (37 km/h)

Armament and payload

• Strike tubes: Up to 22 large vertical payload tubes
• Cruise missiles: Up to 154 Tomahawk land-attack missiles in seven-missile canisters
• Torpedo armament: Mk 48 torpedoes
• Torpedo tubes: Four 533 mm tubes
• Special-operations facilities: Two lock-out chambers capable of supporting Dry Deck Shelters

Related equipment

The Virginia-class Block V attack submarine is intended to recover part of the payload capacity lost as the Ohio-class SSGNs retire. Its Virginia Payload Module adds four large vertical tubes, but a Block V boat is expected to carry substantially fewer Tomahawks than an Ohio-class SSGN. The first Block V submarine fitted with the module was expected to enter service in 2028.

The Columbia class is being developed to replace the Ohio-class ballistic-missile submarines, not the converted SSGNs. Proposals have considered a large-payload submarine derived from the Columbia design, but the available material does not identify an approved direct replacement for the Ohio-class SSGN.