Notes: 

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.

	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.