Homing instincts

Torpedoes are changing to meet the demanding requirements of the littoral environment. Richard Scott surveys current programmes.

The end of the Cold War has pre-cipitated a radically altered anti-submarine warfare (ASW) environment. The one-time emphasis on detecting and prosecuting fast, deep-diving nuclear-powered boats has diminished markedly: the threat today is from quiet conventional submarines operating in the shallow - and acoustically poor - waters of the littoral.

This sea change is bringing attendant improvements in torpedo technology. Increasingly quiet targets and sophisticated acoustic countermeasures - coupled with the shift in emphasis from deep- to shallow- water operations - are driving many upgrade efforts. Equally, with advanced surface ship torpedo countermeasures likely to be deployed widely inside the next decade, there is also a need to improve the efficacy of the torpedo in its anti-surface warfare (ASuW) mode.

In broad terms, torpedoes can be categorised as either heavyweight (533mm diameter) or lightweight (324mm) weapons. The former are generally embarked aboard submarines, although a limited number of navies deploy 533mm torpedoes from surface ships as anti-ship weapons; lightweights arm helicopters, maritime patrol aircraft and (for close-in ASW self-defence) surface ships.

There are exceptions: Sweden has developed four generations of 400mm torpedoes for ship-, submarine- and air-launched applications; and Russia deploys 650mm-diameter weapons aboard its most modern nuclear-powered attack, cruise missile and ballistic missile submarines.

Torpedo design must take into account several considerations: speed (at least 50 per cent faster than the target, as a rule of thumb), operating depth (both maximum and minimum), endurance, quietening, reliability, and cost (initial and through-life). The trade-offs that inevitably result are products of the particular operational requirements and fiscal constraints imposed on the developer.

Torpedo propulsion options can be split into electrical (batteries) and thermal (using mono-propellant, bi-propellant or chemical combustion to raise steam, which then drives an engine). Electric propulsion (usually based on silver-zinc [Ag-Zn] or magnesium silver chloride [Mg-AgCl] batteries) has traditionally been regarded as the most discreet, and thus best able to delay target alertment. Various European studies are currently looking to exploit the increased power density of silver-oxide aluminium (Al-AgO) batteries.

However, the radiated noise produced by modern thermal systems (driving quiet pump-jet propulsors) is now comparable to that produced by battery-driven types at equivalent speeds. Moreover, thermal propulsion provides a much higher maximum speed when called for.

Much effort is being devoted to the development of a homing system (emphasising active operation) capable of reliably detecting and classifying quiet, low-Doppler submarine targets in shallow waters. While multibeam transducer technology continues to evolve, the real gains lie with advanced signal processing - pulse coding of individual beams being an obvious example - designed to discriminate targets from background noise, bottom and surface reverberations, and defensive countermeasures.

Passive acoustic homing has generally been employed against surface ships. Another option, wake-homing, has been used in Russian torpedoes for some time and is now being offered as an adjunct capability in several European types. The latter technique uses an upward-looking sonar beam to detect wake boundaries and then follow the two-dimensional cone to its apex.

Further tactical advantage is gained by the use of wire-guidance, a feature of most contemporary submarine- and ship-launched heavyweights. This allows the torpedo's guidance system to receive course correction updates on the position of a moving target, benefiting from the superior sensor data available from the firing platform. Furthermore, with two-way guidance, the torpedo is itself able to function as a propelled offboard sonar sensor.

Another major trend is the increasing use of commercial-off-the -shelf (COTS) components to improve performance and cut costs. Industry-standard COTS hardware is being exploited for guidance and control functions (replacing bespoke MIL-SPEC tactical computers) and signal processing (executing the demanding software applications required for shallow-water detection and classification). Receiver and transmitter subsystems will also leverage COTS innovation.

At the start of 1997, the US could boast three qualified torpedo manufacturers: Northrop Grumman (now the subject of a proposed acquisition by Lockheed Martin) which had acquired the defence operations of Westinghouse in 1996; Alliant Techsystems; and the Naval and Maritime Systems (NAMS) division of Hughes Aircraft.

However, in March this year Hughes concluded the purchase of Alliant Techsystems' Marine Systems Group (MSG), the latter's torpedo activities being merged with those of Hughes to form the Mukilteo Operations unit of NAMS. Hughes is now itself being purchased by Raytheon.

Following delivery of the last new-build weapon in December 1995, the US Navy has embarked on a programme to update the Mk 48 ADCAP (Advanced Capability) heavyweight torpedoes to improve performance against both open-ocean and shallow-water targets. Under the so -called MODs programme, Northrop Grumman (then Westinghouse) has developed the propulsion upgrade (a muffler which can be turned on or off on command to reduce radiated noise from the OTTO-fuelled swashplate piston engine), while Hughes is responsible for guidance -and-control section improvements (which introduce COTS processors and a new receiver).

The US Navy plans to implement the MODs update across its entire 1,400-plus warshot inventory. The US Naval Sea Systems command has selected Northrop Grumman to undertake the first three fiscal years' (FY96-98) production. The most recent (FY97) award, valued at US$16 million, covers the supply of 135 propulsion-modification and guidance-control kits, plus 100 warhead electronic systems.

An associated Block III software modification for Mk 48 ADCAP will shortly achieve initial operating capability. A Block IV update will follow in 1999.

Hughes, through the NAMS business unit, has been approved to sell the MkE48 ADCAP to selected international navies. MkE48 Mod 4 is in service with the submarine flotillas of Australia, Canada and the Netherlands: MkE48 ADCAP is being offered to the latter to meet Project SEA 1429.

Seahuntor for export

Before its acquisition by Hughes, Alliant Techsystems' MSG had undertaken a series of iterative updates of the 1950s-vintage MkE37. Staged improvements to the basic MkE37 have introduced OTTO-fuel propulsion (designated NT 37C), new acoustics (NT 37D) and a new control and guidance section (NT 37E).

The NT 37F upgrade package, ordered by Egypt for its modernised 'Romeo' class submarines, builds on the NT 37E, offering extended speed and range, increased sonar sensitivity and a far lower maintenance requirement than the original MkE37. Key facets include the introduction of digital and programmable torpedo tactical control logic; additional anti-ship run patterns; a new signal processor; replacement of the Ag-Zn batteries by an OTTO-fuel engine, increasing speed by 40 per cent and range by 150 per cent; and baffling material and a new nose shape to protect the transducer from self-noise, offering a near-100 per cent improvement in shallow-water passive and active detection range.

With several thousand MkE37/NT 37 warshot rounds still in service worldwide, NAMS remains committed to supporting the NT 37 series for a further 25 years. It is also continuing to offer a development of the NT 37 in the shape of the Seahuntor. Effectively the NT 37G in lineage terms, Seahuntor is a further evolution of the NT 37F incorporating a high-energy two-speed OTTO engine, programmable digital control logic, improved signal processing and an enlarged warhead with a new STN Atlas Elektronik proximity fuze.

Two other Seahuntor-derivative developments have been publicised by NAMS. The first is the short (3.2m) Seahuntor(S) variant, two of which can be accommodated on a standard weapon handling rack. The second is SeaArrow, a hybrid heavyweight that mates the MkE48 shell, warhead and propulsion system with Seahuntor guidance and control electronics.

Production of the US Navy's MkE50 advanced lightweight torpedo was ended in FY96. A total of 1,063 weapons was delivered by dual sources Westinghouse and Alliant Techsystems through a five- year period of low-rate initial production.

Powered by a SCEPS (stored chemical-energy propulsion system) engine, the MkE50 is equipped with a directed charge warhead and offers superior speed and depth capabilities to counter fast, deep- diving threats. It is also capable of engaging periscope depth targets.

However, fiscal constraints and changing operational requirements resulted in the early curtailment of MkE50 production. Instead, the US Navy's new lightweight torpedo strategy seeks to leverage the existing warstock of MkE46 and MkE50 weapons, modifying the inventory through selective technology insertion to improve capability against shallow-water threats.

Enter LHT

In 1993, OPNAV directed that a cost and feasibility study should be carried out to assess the practicality of merging the best aspects of the ubiquitous MkE46 torpedo (its reliable and relatively inexpensive propulsion system) with the sophisticated electronics of the MkE50 to create a Lightweight Hybrid Torpedo (LHT).

Accordingly, a control and acoustic test vehicle was assembled to validate vehicle control and stability, and the mechanical, electrical and software interfaces between the MkE46 afterbody and MkE50 forebody.

A subsequent cost and operational effectiveness analysis concluded that a mixed lightweight torpedo inventory, comprising the MkE50, MkE46 Mod 5A(S), MkE46 Mod 5A(SW) and LHT offered the most cost-effective way to meet the evolving littoral threat. As a result, the entire MkE46 Mod 5 inventory and a substantial portion of the MkE46 Mod 5A(S) inventory will be drawn down to provide assets for the MkE46 Mod 5A(SW) upgrade and LHT remanufacture programmes.

The Mod 5A(SW) version of the MkE46 is being introduced in a series of upgrades that began last year. (This was originally part of a service life extension programme [SLEP] to ensure that the design remains maintainable up to 2017.) It confers a limited shallow-water capability by adding a bottom-avoidance capability and improved shallow-running countermeasures; it also corrects an aft seal leakage problem.

A Block Upgrade 1 update is now being introduced for the MkE50. This software modification will further improve shallow-water performance.

In June 1996, the US Naval Sea Systems command awarded Alliant Techsystems MSG, teamed with Hughes, a US$13.2 million contract to develop the LHT. NAMS Mukilteo Operations has become custodian of the LHT contract following Hughes's acquisition of MSG.

LHT - formally designated as MkE46 Mod 8 - will mix components from existing MkE46, MkE48 ADCAP and MkE50 weapons with selected COTS electronics. Principal subsystems include the nose array and transmitter from the MkE50, the MkE103 warhead and propulsion system from the MkE46 (the latter modified to incorporate the MkE50's thermal battery and dual-winding alternator), and the variable-speed control valve from the MkE48 ADCAP heavyweight.

Major COTS components comprise a digital receiver, depth sensor, and signal and tactical processors running MkE48 ADCAP and MkE50 tactical software (developed by the Naval Undersea Warfare Center at Newport, Rhode Island). The LHT will also require a new shell and power converter.

A total of 31 LHT engineering development models will be produced under the development contract, testing of which will culminate in an operational evaluation in 2001. Low-rate initial production could start as early as 1999, with full production following from 2002.

Hughes will apply for LHT export release (as an upgrade to existing MkE46 inventories) on completion of OPEVAL. In the meantime, the company is continuing to offer MkE46 update packages to international customers based on the US Navy's SLEP programme: three countries have already contracted.

The Franco-Italian Eurotorp GEIE, a joint venture between Whitehead Alenia Sistemi Subacquei (WASS), DCN International and Thomson Marconi Sonar, completed qualification testing of the MU 90 Impact lightweight torpedo in mid-1996. However, the award of main production contracts from the French and Italian navies, originally planned for last year, remains pending.

MU 90 is a result of the May 1991 merger of the DCN Murene and Whitehead A290 lightweight torpedo development programmes. In essence, it brings together the acoustic homing head and battery of Murene and the A290 warhead and afterbody section. Tactical software is being developed jointly: the guidance and control system itself is the responsibility of WASS.

The homing head, developed by TMS in Sophia Antipolis, uses the Mangouste signal processor to perform target detection, classification and countermeasures discrimination. Multiple lobing, employing constant or modulated waveforms, is used to overcome problems presented by reverberation and multiple false echoes.

Two warheads are available for Impact. A directed-energy hollow-charge type is optimised for ASW, while a semi-directional high-explosive warhead is for use against surface vessels.

Power for MU 90 is powered by Al-AgO battery with a potassium hydroxide electrolyte. This powers an STN Atlas Elektronik stepless variable-speed electric motor driving a pump-jet propulsor.

According to Eurotorp, speed can be varied from 29kt to a maximum of more than 50kt. The consortium claims that Impact is effective against targets at periscope depth down to beyond 1,000m.

Around 20 pre-production Impact rounds have been produced during the programme's development phase. At-sea qualification trials began in mid-1994 and were completed in July 1996. These included launches from ships, helicopters and maritime patrol aircraft at test facilities in La Spezia and Le Levant.

Eurotorp has already developed Impact-compatible fire-control and launch systems. The new weapon will also be carried as the payload of the MILAS surface-to-underwater guided weapon system being developed for the French and Italian navies.

Germany is expected to be the first export customer for Impact. Meanwhile, Eurotorp is studying an anti-torpedo torpedo variant - known as MU 90HK (Hard Kill) - as part of the NATO Project Group 37 Surface Ship Torpedo Defence System study. Eurotorp is also responsible for continued marketing and production of the Whitehead-developed A244/S Mod 1 lightweight.

DM2A4 in development

In 1992 France, Italy and Germany began a joint feasibility study (undertaken by what was then STN Systemtechnik Nord, DCN Saint Tropez and Whitehead plus a number of other subcontractors) to examine candidate propulsion systems for a putative pan-European heavyweight torpedo. This 24-month feasibility phase, lasting until late 1994, examined three options: high- and low-speed electrical motors powered by a Al-AgO battery; a two-stage Wankel diesel engine; and a semi-closed cycle thermal propulsion system using lithium-based propellant and oxidizer technologies.

The subsequent joint evaluation favoured the development of an electrical system on the grounds of low risk and cost effectiveness. However, France and Italy did not proceed into a planned joint definition phase. Instead, starting in 1995, Germany proceeded independently with the definition of its new DM2A4 heavyweight, with the aim of having the weapon ready for the weapon system technical evaluation of the new U 212 submarine in 2002.

DM2A4 is based on the earlier DM2A3 Seehecht (itself an upgrade of the earlier DM2A1) and as such represents the second part of a two-stage heavyweight inventory update programme begun in the 1980s. Whereas DM2A3 is principally an electronics modernisation incorporating some additional noise-reduction measures, DM2A4 represents a complete propulsion upgrade with accompanying improvements in guidance (using fibre-optics rather than copper wire to provide for the weapon's extended range) and torpedo counter-countermeasures performance. Elsewhere, existing DM2A3 subsystems will be used with only minor modifications required to the homing head, navigation system, communications, fuzing, warhead and exploder.

STN Atlas Elektronik completed the definition phase for DM2A4 in November 1996. In September this year the company was awarded a DM86.9 million (US$48.9 million) contract to undertake full- scale development, which will include the delivery of pre-production torpedoes for service qualification. An earlier con-tract awarded in 1996 had funded critical long-lead items.

Warshot battery technology for DM2A4 will be based on the Al-AgO technology already developed for the Franco-Italian MU 90 lightweight. The new electric motor, which will drive a skewed contra-rotating propeller, is a stepless permanent-magnet DC motor producing 275kW. According to STN Atlas Elektronik, this will provide a 50 per cent increase in maximum speed and a fourfold increase in energy content for the DM2A4.

In-water testing of DM2A4 is due to start in 1999/2000. A full production contract is expected to follow in late 2001. Deliveries of DM2A4 warshots to the German fleet will begin in 2003.

Its progenitor, DM2A3, completed qualification on the German Navy's Type 206A submarines in February 1995 after a trials and evaluation programme that included around 20 firings from trials boat U 23. The Royal Norwegian Navy has also acquired the DM2A3 for its Ula class submarines.

DM2A3 introduced the TOSO acoustic homing head (manufactured by WASS); new two-way wire guidance; a new course attitude reference gyro system; and measures to cut radiated self-noise significantly The latter include new skewed propellers and elastic motor suspension.

The export version of DM2A3 is known as Seahake, while the DM2A4 export variant will be marketed as Seahake Mod 1. STN Atlas Elektronik's SUT heavyweight is still in production for export applications, while Indonesia produces the weapon under licence.

Advancing A184

With Germany proceeding unilaterally on DM2A4, Italy and France are now set to collaborate on the development and production of an fourth-generation A 184 heavyweight torpedo. The two navies hope to agree a joint technical specification by the end of this year, which will be paralleled by an industrial accord between WASS and DCN. A bilateral memorandum of understanding and development contract should be signed in mid-1998.

The collaborative development programme will adopt the Al-AgO battery technology that has already been developed for the MU 90 Impact lightweight torpedo. Other co-developed components include a fibre-optic guidance link and spool, a new electric motor and a skewed propeller.

The A184 Advanced will also incorporate the new ASTRA acoustic homing head, development of which was started by WASS earlier this year under a separate national development programme. ASTRA will use a multibeam planar array with digital pulse compression in any transmission mode, multi-frequency operations in both active and passive modes, and independent processing of each frequency (active and passive) on each lobe.

Development of the A184 Advanced is due to complete in 2002. Current plans call for the first production deliveries to follow in 2004.

The A184 Advanced will be carried aboard the Italian Navy's new Type 212A submarines alongside the A184 Mod 3, development of which began in 1990. An upgrade to the Italian Navy's inventory of A184 Mod 0 and Mod 1 rounds, the Mod 3 package is a combined capability upgrade and life extension designed to ensure the weapon's operational effectiveness through to 2025.

The Mod 3 programme is designed to reduce radiated noise, add a wake-homing capability, upgrade homing performance and improve countermeasures resistance. A digital fire-control interface is added, and the torpedo is now compliant with NATO STANAGs.

Modifications comprise the integration of the TOSO acoustic homing head and its associated classification software, a wake-homing sensor (also part of the A184 Advanced programme), replacement of the wire-guidance electronics, a new Ag-Zn battery, a low-noise skewed direct-drive propeller and a longer guidance wire. New automatic test equipment is also introduced as part of the package.

A184 Mod 3 development and qualification has been completed after extensive at-sea trials. WASS is negotiating with the Italian Navy to start the upgrade of batches of existing A184 warshots from 1998.

The F 17 Mod 2 wire-guided heavyweight, manufactured by DCN Saint Tropez, remains available for export. The current production baseline Mod 2B features a new nose assembly and active/passive homing head, a new exploder and an all-digital guidance and control unit.

Mod 2B uses a brushless, low-speed synchronous motor to reduce radiated noise. Its warhead contains 250kg of Cast PBX explosive, equivalent to 450kg of TNT.

F 17 Mod 2 is powered by a PB32 Ag-Zn battery for a maximum range of 29,000m. It runs at two speeds: 18km at a quiet 28kt, followed by 11km at 40kt. Maximum effective depth is around 600m.

DCN has advertised a wake-homing modification for the F 17 Mod 2, incorporating an STN Atlas Elektronik Acoustic Wake Detector (AWD) system as an adjunct to the existing acoustics. The AWD would be fitted in a 150mm compartment just aft of the transducer.

DCN Saint Tropez, in conjunction with SAFT, has developed a replacement PB47 Ag-Zn primary battery intended as a modernisation option for the SUT and SST4 heavyweight torpedoes. The activation sytem is the responsibility of DCNSaint Tropez, while SAFT is industrial partner for the electrochemical cells.

The Gidropribor Central Scientific Research Establishment in St Petersburg has been responsible for the design and development of all Russian ship-and submarine-launched torpedoes. Manufacture has been largely concentrated at the Dvigatel plant in St Petersburg, although the 53-65KE is sourced from Mashzavod in Almata, Kazakhstan. Manufacture of the now-obsolete SET-40, SET-65 and SAET -60M straight-running torpedoes was undertaken by the Dazigel JSC in Dagestan.

Dvigatel is marketing the electrically powered TEST-71ME and UTEST-71E wire-guided 533mm heavyweights for export. An evolution of the earlier SET-65 series, the TEST-71ME anti-submarine weapon can be launched from both ships and submarines and has a range of about 20,000m.

UTEST-71E adds a wake-homing capability to the standard active/passive acoustic homing of TEST-71ME to provide a dual-mode capability. TEST-96 is a further development, which incorporates an improved homing head.

TEST-71ME forms part of the standard torpedo load-out for export Project 877EKM and Project 636 'Kilo' class submarines alongside the 53-65KE anti-surface vessel weapon. The latter is powered by a bi -propellant: the combustion of kerosene in oxygen produces steam to power a Morteplotekhnika 2DT gas turbine driving contra-rotating propellers, giving warshot torpedoes a range of 19,000m.

The 53-65KE is fitted with a wake-homing (upward-looking) active acoustic sensor. Its 305kg warhead is activated by an electromagnetic proximity fuze when the torpedo is beneath the keel of the target vessel.

Other electrically powered ship- and submarine-launched weapons advertised by Gidropribor in recent years include the USET-95 (a 400mm ASW/ASuW weapon) and TE-2 (a 533mm dual-mode wire-guided torpedo with an active/passive seeker head and wake-homing). The UGST, currently in development, is believed to be a new wire-guided active sonar/wake homing 533mm torpedo powered by a Morteplotekhnika APD gas turbine.

Uniquely, Russia has also developed and fielded 650mm submarine-launched wake-homing torpedoes. A turbine-powered DST-92 variant has been offered for export.

In July 1996 the UK Ministry of Defence awarded the Underwater Weapons Division of GEC-Marconi (now part of the company's Radar and Defence Systems business) a Pds109 million (US$178 million) contract for the full development and pre-production phase of the Sting Ray lightweight torpedo life extension and capability update. The programme, against SR(SA) 7589, will bring current UK Royal Navy (RN) and Royal Air Force (RAF) Mod 0 weapons up to an improved Mod 1 standard for a service life to 2020.

Sting Ray update

The Mod 1 will retain the essential dynamic and propulsion features of Mod 0, but will feature new tactical and acoustic processing hardware in the form of a new digital correlator (based on SHARC boards), an improved front-end sonar (with a new active section) and a solid-state autopilot.

Software development will continue, with a focus on improved performance against quiet targets in shallow water. Mod 1 will also introduce digitally controlled electric (rather than hydraulic) actuators and new-production Mg-AgCl batteries.

Between 50 and 100 Mod 1 warshots are being produced as part of the development phase. A main production order (MPO) for the progressive conversion of existing RN/RAF Sting Ray warshots to Mod 1 standard is expected by the end of 2002. Target in-service date is 2004.

Sting Ray has been exported to Egypt, Norway and Thailand. It is expected that GEC-Marconi will offer upgrade proposals to its existing customer base.

The much-delayed Pds630 million (US$1.03 billion) MPO for the RN's Spearfish heavyweight torpedo was placed with GEC-Marconi in December 1994. Running through to 2004, the MPO also includes provision for the weapon's in-service support (ISS) function.

The MPO is thought to cover the delivery of about 350 warshot torpedoes, much reduced from the 1,000 rounds envisaged in the late 1980s. The Royal Naval Armament Depot (RNAD) at Beith will have responsibility for final assembly, integration and test. ISS work will also be undertaken at Beith.

Procured against SR(S) 7525 as an advanced heavyweight intended to replace the Royal Navy's current MkE24 Mod 2 Tigerfish torpedo, Spearfish is powered by a Sundstrand 21TP01 gas turbine (using HAP -OTTO fuel) driving a shrouded pump-jet propulsor. Speeds of more than 65kt have been achieved during trials.

Spearfish can operate at a range of speeds, and is claimed to be as quiet as the battery-powered Tigerfish when running slow. Noise-reduction measures stem from previous experience with Sting Ray and from extensive modelling of engine, exhaust and flow noise.

Spearfish's acoustic processing and tactical control software draws on Sting Ray Mod 0 experience, but is executed on more modern processing hardware. The homing system hosts around 200,000 lines of operational code, and is capable of both wire-guided and autonomous attacks.

A contract for full development and production of an initial 100 Spearfish torpedoes (some of which have since been expended in trials) was placed in 1981. However, deliveries were at one stage suspended because of reliability problems.

The Spearfish MPO was repeatedly deferred by budget pressures, successive defence reviews and unsuccessful attempts to run a prime contract competition. The requirement to implement a reliability assurance programme delayed the programme for a further three years.

Fleet Weapon Acceptance was eventually achieved in 1994, six years behind Spearfish's original in-service date. Development and initial production costs are estimated at about Pds1 billion (US$1.6 billion).

Spearfish will have totally replaced the RN's current warstock inventory of MkE24 Mod 2 Tigerfish heavyweight torpedoes by the end of 2003. However, Tigerfish remains available for export (a second batch of Mod 2 weapons is in production for Turkey) and GEC-Marconi is committed to supporting the weapon until at least 2015.

Acknowledging that the absolute capability and infrastructure requirements of Spearfish will put it at a price disadvantage on the international market, GEC-Marconi is examining the development of a putative Tigerfish Mod 3 variant as a more affordable export product.

The concept, for which studies began in mid-1996, envisages a hybrid design that would marry the proven dynamics and electric propulsion of Tigerfish (but swapping hydraulic actuators for electric) with new COTS-based signal processing technology from Sting Ray Mod 1, plus some inputs from the guidance and homing software used in Spearfish.

If GEC-Marconi proceeds with production investment in Tigerfish Mod 3, the existing Tigerfish customer base (Brazil and Turkey) is likely to be offered upgrade kits to bring their existing weapons up to the improved standard.

Bofors Underwater Systems began initial development of the new Torpedo 2000 heavyweight in 1988, with a full-scale development contract awarded in 1991. Verification trials for the Royal Swedish Navy (RSwN), which has given Torpedo 2000 the service designation Tp 62, have been completed. A production order is expected in the near future.

Designed to replace the current Tp 613 anti-ship heavyweight on board RSwN submarines and missile boats, the wire-guided Torpedo 2000 has been developed against a stringent Swedish Defence Materiel Administration (FMV) specification. This included requirements to reduce length by at least 1m compared with the 7m Tp 613, and to reduce weight by at least 500kg from the earlier weapon's 1,850kg mass, while at the same time providing equivalent or greater warhead effect. FMV also required that the new torpedo should offer significant increases in speed and range, deeper diving capability and reduced radiated noise.

After studying various electrical and thermal propulsion options, Bofors selected a bi-propellant solution: a combination of 85 per cent High Test Peroxide (HTP) and 15 per cent kerosene.

The HTP decomposes in a chamber, with the aid of catalytic silver nets, to produce oxygen and steam at 600C. This is fed to a gas generator, where the kerosene is injected and fresh water added to cool the system, resulting in a greater volume of exhaust gas at 750C. This drives a seven-cylinder piston engine. Exhaust, mainly steam and carbon dioxide, pass through a condenser and most of the condensate is recycled. The remainder is compressed before release into the sea.

The propulsor itself is a pump-jet based on that used in the UK's Spearfish heavyweight. Torpedo 2000 can trade off speed against range up to a maximum of about 50kt and 50,000m respectively.

Transducer arrays are positioned in a recess in the nose, with signal processing executed in the electronics section just aft. Three selectable modes are available: active, passive and simultaneous active/passive.

Development of the wire-guided Torpedo 43X2 (designated as Tp 45 by the RSwN) was begun by FFV (now subsumed within Bofors Underwater Systems) in 1990. Launched from helicopters, ships and submarines, it is the RSwN's fourth generation of 400mm weapon (a lineage that dates back to the Tp 41 of the early 1960s). Primarily an ASW weapon, it also has an anti-surface capability.

Torpedo 43X2 is itself an upgrade of the earlier 43X0, replacing the earlier homing head with a new multimode (active, passive and simultaneous active/passive) transducer and signal processor essentially identical to that fitted to Torpedo 2000. Optimised for shallow-water conditions, it is claimed to be able to track multiple targets against a background of environmental noise and acoustic countermeasures.

Power is supplied by an Ag-Zn battery unit feeding a geared DC electric motor via a thyristor switch. One of three different run speeds can be selected.

Tp 45 deliveries to the RSwN began in 1993. Pakistan is the only export customer to date, ordering Torpedo 43X2 in 1994 for retrofit to four ex-RN Type 21 frigates.

Bofors Underwater Systems was awarded a project-definition (PD) study by FMV in mid-1996 to define the next-generation Torpedo 46 (Tp 46) lightweight torpedo (alternatively known as Torpedo 90). The Danish Naval Materiel Command is contributing a share of funding under an agreement with FMV for joint development of Tp 46: low-level study work on a new lightweight has been under way in FMV since 1992.

Although drawing on experience from the existing Torpedo 43X2, and retaining the 400mm diameter of its forebear, Bofors says that Tp 46 will be an all-new torpedo intended to offer very high detection and classification performance in both shallow-water and open-ocean environments. The propulsion system will use a thermal battery system, a brushless motor (offering stepless speed control) and a pump-jet propulsor.

Tp 46 will use a fibre-optic link for two-way communications between the launch platform and the torpedo. A radio buoy will be used as a relay for air-dropped weapons.

The full Torpedo Weapon System 90 will also include a platform torpedo interface, launch system and a logistic support package. On current plans, Tp 46 is expected to enter full development in early 1998, entering operational service around 2005. The export variant will be known as Grampus.

A number of other countries have embarked on efforts to develop indigenous torpedo manufacture, remanufacture or upgrade lines.

South Africa's Institute of Maritime Technology (IMT) has developed the A44 lightweight torpedo, essentially a MkE44 body fitted with a directed energy warhead and a new homing system. IMT is also believed to have worked on a South African heavyweight development derived from the French-supplied E 14.

South Korea's Agency for Defence Development is managing two indigenous development programmes: the Blue Shark lightweight and the White Shark heavyweight. Eurotorp is reported to have been contracted to provide technical assistance for the Blue Shark programme, which may use the existing MkE44 as its baseline. White Shark is reported to leverage NT 37 technology.

Japan is introducing the Type 89 heavyweight, manufactured by Mitsubishi, to complement its existing Type 80 inventory. Analogous to the MkE48, it uses thermal propulsion and has a range of approximately 30,000m.

In 1986 it was announced that the NST-58 lightweight torpedo, developed by India's Naval Science and Technology Laboratory in Vishakhapatnam, had been put into production. The NST-58 is generally assumed to be a derivative of the Whitehead-supplied A244/S.