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2 February 2001
Background Information: Mk 48 ADCAP

Link to slideshow of Mk 48 ADCAP test

Submarine-launched dual-purpose torpedo.

Anticipation by the US authorities of impending advances in submarine technology by the former USSR, noted in the 1960s and 1970s, led to studies of the Mk 48's capabilities against likely threats. In 1975 an Operational Requirement was issued by the Chief of Naval Operations for a programme to develop appropriate modifications to the Mk 48 torpedo to allow it to keep pace with anticipated submarine threat developments. The origins of the Mk 48 ADCAP (advanced capabilities) programme lay in this requirement, but the extent and rate of Soviet submarine technology advance hastened both ADCAP progress and another Mk 48 improvement programme.

Recognition (by the USA) of the impressive operational characteristics of the former Soviet `Alfa' class submarine in late spring 1979 resulted in a decision, taken in September 1979, to accelerate the ADCAP programme. It was also responsible for an intensive test and analysis programme to determine the true limits of the then current Mk 48 in terms of depth, speed and acoustic capabilities. This was known as the expanded operating envelope programme. Moreover, it showed that the Mk 48 was structurally reliable at the depth needed to engage `Alfa' class submarines. It also showed that the target speed recognition capability required could be achieved, that the vertical coverage was adequate, as was the self-noise at higher speeds with the existing nose and array, and that additional speed could be achieved. Laboratory modifications were made to a few torpedoes for tests and these changes were implemented in the form of a programme to update fleet Mk 48 torpedoes to what is now the Mk 48 Mod 4 standard.

Of the performance requirements demanded by the ADCAP programme, the most important are:

- sustained long acquisition range
- minimised adverse environment and countermeasure effects
- minimised shipboard tactical constraints
- enhanced surface target engagement capabilities.

Hardware changes involved in ADCAP entail replacing the entire nose of the weapon housing the acoustics and beam-forming circuits, and replacement of the signal processing by the latest electronics. The latter will also incorporate the current command and control electronics. Warhead sensor electronics will be improved.
Application of the expanded operating envelope programme findings to ADCAP has resulted in the upgraded ADCAP, which incorporates: upgraded acoustics and electronics; an expanded operating envelope (depth, target speed, weapon speed options); increased fuel delivery rate and capacity for optimum speed and endurance; improved surface target capabilities.

The torpedo is wire-guided through a two-way communications link in the current Mod 3 version.

The Mk 48 torpedo is propelled with an axial flow pump jet propulsor with twin contra-rotating propellers driven by an external swashplate combustion gas piston engine. This engine, like that in the Mk 46 torpedo, is a Gould design. The fuel for the engine is a monopropellant: Otto fuel II which uses nitrogen ester and an oxidant.

The Mk 48 and Mk 48 ADCAP torpedoes are capable of operating with or without wire-guidance using active and/or passive, acoustic homing. On launching, the weapon executes a programmed target search, acquisition and attack procedures, with the capability to conduct multiple re-attack procedures if the target is missed. The seeker has an active electronically-steered `pinger' that enables the torpedo to avoid having to manoeuvre as it approaches its target.

The Mk 48 ADCAP Mod 6 (MODS) features two hardware upgrades: the guidance and control upgrade and the torpedo propulsion upgrade. The guidance and control upgrade replaces the obsolescent guidance and control unit with current technology, improves the acoustic receiver, and adds additional memory and improves processor throughput to handle the expanded software demands anticipated for near term upgrades. The torpedo propulsion upgrade improves the propulsion unit, details of which are classified.

Included in the upgrade is a Common Broadband Advanced Sonar System (CBASS) programme, which will develop a fully digital wideband sonar capability to enable the torpedo to operate effectively both in shallow water (<180 m) to counter diesel electric submarines operating in the littoral and deep water environments. For this the torpedo will also feature frequency agility and optimal frequency selection. This capability will allow the Mk 48 ADCAP to identify torpedo countermeasures and discriminate them from the target. Full rate production of this upgrade is scheduled to begin in FY04.

The Stealth Torpedo Enhancement Program (STEP) will be introduced in two phases. Phase 1 will build on the CBASS capability providing guidance upgrades and eliminate sonar footprints, while Phase 2 will see stealthy and higher power density propulsion improvements and an upgraded warhead.

Operational status
The Mk 48 has been in production since 1972 and is used aboard USN attack submarines and strategic submarines for self-defence. By early 1980, more than 1,900 torpedoes of this type had been delivered to the USN and an estimated 800 plus were in the production and procurement line. It was then estimated that another 1,050 might be required to meet inventory objectives and to allow for peacetime training and testing.

In August 1979, Hughes Aircraft Company received a contract for development of digital guidance and control electronics for the Mk 48 ADCAP programme.

The first test run was carried out by the USN at Nonoose Bay in early 1982, using the inertial guidance system developed for the ADCAP programme. About 240 more runs were programmed before completion of this phase of the programme, after which it was expected that entry into service would take place in 1983-84. However, the 1985 report by the US Secretary of Defense amended this to indicate anticipated deployment of the system in the mid- to late-1980s.

In the US Secretary of Defense's Annual Report to Congress in February 1985, it was stated that following completion of a successful test programme in 1984, it had been decided to accelerate production of the ADCAP torpedo. The five year programme called for production of 1,890 ADCAP units and included 123 in 1986 at a cost of US$433 million and 280 units in 1987 costing US$671 million. Hughes began production of the ADCAP version in 1985 and it became operational in 1988. In 1986, Gould (subsequently taken over by the former Westinghouse Company) was named the second ADCAP source.

Hughes Aircraft Company was awarded contracts for 370 plus Mk 48 ADCAP torpedoes and related test equipment, and the former Westinghouse Electric Corporation a contract for 96 Mk 48 ADCAP. In June 1989, the US House Armed Services Seapower subcommittee cut US$331 million from the US Navy's US$493 million procurement request for Mk 48 ADCAP for 1990, reducing the proposed buy from 320 to 140 for 1990. At the beginning of 1989, the Pentagon had approved ADCAP for full-rate production. In mid-1992, Hughes Aircraft Company was awarded a US$183 million contract to manufacture 324 Mk 48 ADCAP weapons over a five year period. This contract eliminated the second source supplier, leaving Hughes as the sole supplier of the Mk 48 ADCAP. Final deliveries of Mk 48 ADCAP were conducted under the FY94 programme. In mid-1995, the then Westinghouse Company won a four year contract to retrofit 450 Mk 48 ADCAP torpedoes. The upgrade includes COTS microprocessors, improved receivers and improved quieting of the propulsion system involving the fitting of a muffling device to the motor, which will be activated prior to launch. This will improve the weapon's performance in littoral regions. The Mk 48 ADCAP is to undergo a Block IV upgrade commencing in 1999. The Navy will acquire about 1,046 MODs ADCAPS (Mod 6) replacing an equivalent number of Mod 5 ADCAPS, and maintaining the total inventory of ADCAP torpedoes at 1,046. The only known foreign users of the Mk 48 are Australia, Canada, Israel, Netherlands and Turkey (in ex-US Navy submarines).

Length: 6,100 mm
Diameter: 533 mm
Weight: 1,814 kg
Warhead: 267 kg
Max speed: 55 kt
Range: 38 km at 55 kt or 50 km at 40 kt
Max depth: 800 m

Raytheon Systems Company, Mukilteo, Washington.
Data processor cards which are part of digital guidance and control system being developed by Hughes for Mk 48 torpedo ADCAP programme

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