Ohio Class, Ballistic Missile Nuclear Powered Submarine, USS Kentucky SSBN737

The real Ohio family, specifications & cut-away:

The Ohio class submarines serve the United States Navy as the virtually undetectable undersea launch platforms of intercontinental missiles. The Electric Boat Division of General Dynamics, based at Groton, Connecticut, has built 18 Ohio submarines, commissioned between 1981 and 1997. The submarines of the Pacific Fleet are based at Bangor, Washington, and those of the Atlantic Fleet at King's Bay, Georgia. The submarines spend 70 days at sea followed by 25 days in dock for overhaul. 
Under the requirements of the STrategic Arms Reduction Treaty, START II, which was agreed in June 1992, the number of strategic missile submarines will be limited to 14 from the year 2002. Rather than decommissioning these four submarines, the US Navy plans to convert them to SSGNs (conventionally armed nuclear-powered) submarines. In September 2002, Electric Boat received a contract for the conversion of USS Ohio, Michigan, Florida and Georgia. The submarines will be refitted with up to 154 Tomahawk TLAM (land attack) missiles and will also be capable of conducting special operations missions with accommodation for Advanced SEAL delivery systems (ASDS), mission control center and 102 special operations troops. USS Ohio will rejoin the fleet in 2007. USS Pennsylvania and USS Kentucky will shift homeport from Kings Bay to Bangor to balance the strategic force.

The Ohio family:

Boat: Name: Laid Down: Launch: Commission:
SSBN-726 Ohio 10 Apr 76 7 Apr 79 11 Nov 81
SSBN-727 Michigan 4 Apr 77 26 Apr 80 11 Sep 82
SSBN-728 Florida 9 Jun 77 14 Nov 81 18 Jun 83
SSBN-729 Georgia 7 Apr 79 6 Nov 82 11 Feb 84
SSBN-730 Henry M. Jackson (ex-USS Rhode Island) 19 Jan 81 15 Oct 83 6 Oct 84
SSBN-731 Alabama 27 Aug 81 19 May 84 25 May 85
SSBN-732 Alaska 9 Mar 83 12 Jan 85 25 Jan 86
SSBN-733 Nevada 8 Aug 83 14 Sep 85  16 Aug 86
SSBN-734 Tennessee 9 Jun 84 13 Dec 86 17 Dec 88
SSBN-735 Pennsylvania 10 Jan 84 23 Apr 88 9 Sep 89
SSBN-736 West Virginia 24 Oct 87 14 Oct 89 20 Oct 90
SSBN-737 Kentucky 18 Dec 87 11 Aug 90 13 Jul 91
SSBN-738 Maryland 18 Dec 89 15 Jun 91 13 Jun 92
SSBN-739 Nebraska 26 May 87 15 Aug 92 10 Jul 93
SSBN-740 Rhode Island 1 Dec 90 17 Jul 93 9 Jul 94
SSBN-741 Maine 4 Apr 89 16 Jul 94 29 Jul 95
SSBN-742 Wyoming 27 Jan 90 15 Jul 95 13 Jul 96
SSBN-743 Louisiana 19 Dec 90 27 Jul 96 06 Sep 97
SSBN- An additional six subs was scheduled to be made, but due to defense cut backs, disarmament treaties, and the end of the cold war, they were cancelled.

The Ohio subís specifications & "Cut-Away":

Builders: General Dynamics Electric Boat Division.
Power Plant:
(See additional info at the bottom)
One S8G nuclear reactor core reloaded every nine years, two geared steam turbines, one shaft, output of 60,000 hp
Length: 560 feet (170.69 meters)
Beam: 42 feet (10.06 meters)
Displacement: Surfaced: 16,764 tons  Submerged:18,750 tons
Speed: Official: 20+ knots (23+ miles per hour, 36.8+ kph)    Actual: 25 knots submerged speed
Operating Depth: Official: "greater than 800 feet"    Actual: greater than 1,000 feet
Armament: 24 - tubes for Trident I and II, 4 - torpedo tubes with Mk48 Torpedoes
Sensors: (Please see section below)
Crew: 15 Officers, 140 Enlisted
Pressure Hull Steel Type: HY-80 (Please see below for details)
Unit Operating Cost: Annual Average $5,000,000 [source: [FY1996 VAMOSC]
Date Deployed: November 11, 1981 (USS Ohio)


cutawayohio.jpg (103801 byte)

Click to enlarge

The steel skin of the Ohio family:
The pressure on a submarine's hull increases with depth, limiting the depth below the ocean surface at which it can operate. The water pressure increases by 44.45 pounds per square inch for every 100 feet of additional depth in salt water.

Submarine designers normally intend their creations to operate well away from the hull's physical limits, imposing a safety margin that varies from country to country [1.5 in the USA, 1.75 in the UK, and 2.0 in Germany].

Typically a submarine will have three diving depths:
  • a normal operating or "test" depth
  • a safe excursion depth
  • a crush or collapse depth
A submarine's hull is normally constructed of steel, or exceptionally of titanium. Special High Yield [HY] steel alloys have been developed to increase the diving depth of submarines, although the improved depth performance of these alloys imposes a price of increased fabrication challenges. These special steels are denominated by their yield stress in thousands of pounds per square inch -- thus HY-80 steel has a yield stress of 80,000 pounds per square inch, HY-100 a a yield stress of 100,000 pounds per square inch, and so on.
  • During World War II, American fleet submarines normally operated at a depth of 200 feet, though in emergencies they would dive to a depth of 400 feet.
  • Post-War American submarines, both conventional and nuclear, had improved designs and were constructed of improved materials [the equivalent of "HY-42"]. These boats had normal operating depths of some 700 feet, and a crush depth of 1100 feet.
  • The Thresher, the first American submarine constructed of HY-80 steel, reportedly had a normal operating depth of 1,300 feet, roughly two-thirds the crush depth limit imposed by the HY-80 steel.
  • The Seawolf, the first American submarine constructed of HY-100 steel, is officially claimed by the Navy to have a normal operating depth of "greater than 800 feet," but based on the reported operating depth of the Thresher, it may be assumed that the normaly operating depth of the Seawolf is roughly double the official figure.
  • The Soviet Alfa submarines, constructed of titanium, reportedly had an operating depth of nearly 4,000 feet.

Above: Launch of Trident Missile while submerged.

The Ohio class submarine is equipped with the Trident strategic ballistic missile from Lockheed Martin Missiles and Space. The Trident was built in two versions, Trident I (C4), which is being phased out, and the larger and longer range Trident II (D5), which entered service in 1990. The first eight submarines, (SSBN 726 to 733 inclusive) were equipped with Trident I and the following ten (SSBN 734 to 743) carry the Trident II. Conversion of the four Trident I submarines remaining after START II (Henry M. Jackson, Alabama, Alaska and Nevada), to Trident II began in 2000 and is planned to complete in 2008. Lockheed Martin received a contract in January 2002 for the production of 12 Trident II missiles for the four submarines.

The submarine has the capacity for 24 Trident missile tubes in two rows of twelve.

  The dimensions of the Trident II missile are length 13.60m x diameter 2.10m and the weight is 59,000kg.

The three stage solid fuel rocket motor is built by ATK (Alliant Techsystems) Thiokol Propulsion and provides a range in excess of 11,000km. Missile guidance is provided by an inertial navigation system, supported by stellar navigation.
Trident II is capable of carrying up to twelve MIRVs (multiple independent re-entry vehicles), each with a yield of 100 kilotons, although the SALT treaty limits this number to eight per missile.
The circle of equal probability (the radius of the circle within which half the strikes will impact) is less than 150m. The Sperry Univac Mark 98 missile control system controls the 24 missiles.


Type: 21" (53.3 cm) Mark 48 and Mark 48 ADCAP. 
Date of design About 1970
Date in service, Mark 48: 1972 
Date in service, Mark 48 ADCAP: 1988
Weight, Mark 48: 3,434 lbs. (1545.3 kg)
Weight, Mark 48 ADCAP: 3,695 lbs. (1662.75 kg) 
Overall length 19 ft 0 in (5.790 m)
Explosive charge 650 lbs. (292.5 kg) PBXN-103
This is equivalent to about 1,200 lbs. (544 kg) of TNT 
Range / speed 10,000+ yards (9,000+ m) / 28+ knots 
(Official figures, but see notes below)
Power Piston engine; pump jet 


The Mark 48 is designed to combat fast, deep-diving nuclear submarines and high performance surface ships. It is carried by all Navy submarines. The improved version, Mark-48 ADCAP (for ADvanced CAPabilities), is carried by attack submarines, the Ohio class ballistic missile submarines and will be carried by the Seawolf class attack submarines. The Mark-48 replaced both the Mark 37 and Mark 14 torpedoes. Mark 48 and Mark 48 ADCAP torpedoes can operate with or without wire guidance and use active and/or passive homing. When launched they execute programmed target search, acquisition and attack procedures. Both can conduct multiple re-attacks if they miss the target. 

The non-nuclear approach to the high speed, deep diving submarine was a very fast, deep diving torpedo with a high performance guidance system, that is, a much improved Mark 37 that would take full advantage of post-WW II technology. Consideration of such weapons, both submarine launched and air launched, began in November 1956 as part of the RETORC (Research Torpedo Re-Configuration) program. By 1960 a specific heavy weight torpedo project had emerged and designated first as EX 10 and later as Mark 48. After a bidder qualification exercise and competition between the qualified bidders, a project definition contract was awarded to Westinghouse. A parallel contract was awarded to Clevite for the development of an alternative acoustic system. The Westinghouse contract was subsequently extended to include the development of the turbine powered Mark 48 Mod 0 which had only an ASW capability. Some Mod 0's were produced for evaluation, but by 1967 it had been decided that an anti-surface vessel capability was also needed. Some feeling persists that this was more of a ploy to keep Clevite in the running than a significant operational requirement. 

A competition between the Mark 48 Mod 1, which had emerged in rudimentary form from the Clevite contract, and Mark 48 Mod 2, a redesign of the Westinghouse Mod 0 followed. The Westinghouse torpedo used a Sunstrand turbine, as used in the Mod 0, for propulsion while Clevite used Otto fuel in an external combustion, axial piston engine. One of several selection factors was apparently the better efficiency of the piston engine, especially when running deep, as opposed to the quieter, but less efficient turbine. The acoustic systems were also somewhat different. In 1971 after competitive evaluation a full scale production contract was awarded to Gould15 (formerly Clevite). The first Mark 48 Mod 1 torpedoes were delivered to the fleet in 1972, twelve years after the development characteristics had been approved. 

Frequently published, but unofficial, data indicate that the Mod 0 was capable of 55 knots for 35,000 yards (32,000 m) and could operate as deep as 2,500 feet (760 m), but not at maximum speed. Its acoustic homing system is reported to have an acquisition range of 4,000 yards (3,640 m), about four times that of the Mark 37. This performance is impressive and generally adequate for dealing with 30+ knot, deep-diving targets. 

The combination of substantial on-board capability (HCL) to control search, homing and re-attack maneuvers and wire guidance provides a formidable weapon. The addition of two way communication (TELCON) in the Mod 3 provided data from the torpedo sonar and actual torpedo operating data (course, speed, depth etc.) to the submarine fire control system, thus substantially enhancing performance. Mod 4 added envelope expansion features, including increased speed and deeper diving, and a fire and forget capability. Existing torpedoes were upgraded by kits and Mod 4s were production torpedoes from 1980 on. Mod 5 was an interim upgrade of existing torpedoes pending the availability of ADCAP. The Mark 48 torpedo had teething problems, but it is a very sophisticated, high performance weapon. Published photographs of the destruction of targets attest to its effectiveness. The main technical criticism of the Mark 48 seems to be that it is very noisy. 

Prior to the mid-1960s Soviet submarines had diving depths of 650 to 1000 feet (200 to 330 m) and submerged speeds under 30 knots. Early Mark 48 capabilities were clearly capable of attacking such targets. The advent of the Soviet ALPHA submarine with its non-magnetic titanium hull, 2,500 foot (760 m) diving depth and submerged speed in excess of 40 knots apparently produced a validated threat against which the Chief of Naval Operations issued a new operational requirement in 1975. Two approaches to satisfying this requirement were initiated. The first was the Mark 48 "envelope expansion program" which exploited the capabilities of the existing torpedo. The second was essentially a new torpedo, ADCAP. The major changes in ADCAP involved entirely new digital electronics, inertial guidance (replacing the gyro system), a major reduction in volume devoted to electronics, a corresponding major increase in fuel capacity, a strengthened shell and, of course, inclusion of the Mark 48 envelope expansion features. The Mark 48 piston engine was retained but with a greater fuel flow rate to yield an estimated 63 knot speed. Much of the change was made possible by the introduction of integrated circuits, including microprocessors, whose small size made it possible to move many of the functions of the control group into the nose. The guidance wire spool was moved to a position aft of the enlarged fuel tank and other layout changes were made.

The Ohio class submarine is fitted a Mark 118 digital torpedo fire control system. 


The Ohio class submarine is equipped with eight launchers for the Mk 2 torpedo decoy. Electronic warfare equipment is the WLR- 10 threat warning system and the WLR-8(V) surveillance receiver from GTE of Massachusetts. The WLR-8(V) uses seven YIG tuned and vector tuned superheterodyne receivers to operate from 50MHz up to J-band. An acoustic interception and countermeasures system, AN/WLY-1 from Northrop Grumman, has been developed to provide the submarine with an automatic response against torpedo attack.


Surface Search          BPS 15A I/J band
Navigation BPS 15A
Fire Control CCS Mk2
Mk 98 missile fire control
Mk 118 torpedo control
ESM WLR-8(V)5 intercept
WLR-10 radar jamming
Sonars IBM BQQ 6
Raytheon BQS 13, spherical array for BQQ 6
Ametek BQS 15 (Towed) 
Western Electric BQR 15 (w/BQQ 9 signal processor)
Raytheon BQR 19
Periscopes Kollmorgen Type 152 and Type 82


The main machinery is the pressure water reactor GE PWR S8G with two turbines providing 60,000hp and driving a single shaft. The submarine is equipped with a 325hp Magnatek auxiliary prop motor. The propulsion provides a speed in excess of 18 knots surfaced and 25 knots submerged.

Naval pressurized-water reactors include a primary coolant system and a secondary coolant system. The primary system circulates water, which is pressurized to keep it from boiling, in a closed loop. As water passes through the reactor, it is heated. It then goes through the steam generator, where it gives up its heat to generate steam in the secondary system. Finally, it flows back to the reactor to be heated again. Inside the steam generator, heat energy is transferred across a watertight boundary to the secondary system, also a closed loop. The un-pressurized water in the secondary system turns to steam when heated. The steam, in turn, flows through the secondary system to the propulsion turbines, which turn the propellers, and to the turbine generators, which supply electricity. As it cools, it condenses to water and is pumped back to the steam generator.

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