Sting Ray Lightweight Torpedo

Type

Air-launched, electric-powered, homing torpedo.

Development

This lightweight torpedo is dedicated to the destruction of submarines rather than surface ships. Most modern lightweight torpedoes are descendants of the so-called Mk 24 `mine', introduced during the battle of the Atlantic in 1942, to destroy submarines by homing on their cavitating propellers as they dived.
    The UK's requirement for an indigenous lightweight torpedo began in 1943 when a group of Royal Air Force officers started an investigation into methods of improving attack capabilities on submarines. In 1944, a joint RAF/GEC team was introduced to the staff of the Admiralty's Underwater Development Establishment and work began on a number of underwater weapon programmes. The years between the end of the Second World War and the 1970s saw a succession of false starts in UK lightweight anti-submarine torpedo design. Developments such as the Dealer, or Mk 30 passive homing torpedo and the Pentane, which incorporated active as well as passive homing, were phased out or never entered service. The Mk 31 ran into cost and programme problems and was cancelled in 1970. At this stage the Royal Navy and the Royal Air Force set out their future requirements for a common anti-submarine torpedo in a joint Naval Air Staff Requirement, NASR 7511, eventually to become the 7511 or Sting Ray project. It is worth noting that included in the requirement was a shallow-water (presumably for the continental shelf of the North Sea) capability.
    In 1977 a design contract was awarded to the Underwater Weapons Division of Marconi Space and Defence (later Marconi Electronic Systems, now BAE Systems) and full-scale development started. The first contract was placed in 1979 and the first preproduction weapon was delivered in 1981. Acceptance trials began in 1982, and some early Sting Ray torpedoes were sent to the South Atlantic during the Falklands campaign in 1982, but they were not used. Fleet Weapon Acceptance trials were successfully completed in 1985 when Sting Ray's complete performance envelope was checked out. Subsequent to these trials the RAF carried out the first live-warhead firing: a Sting Ray dropped from a Nimrod aircraft destroyed a double-hulled submarine target moored at a depth of 65 m in the Mediterranean. Sting Ray officially entered service with the UK in 1986 and has been cleared for carriage on several fixed- and rotary-wing aircraft including: Sea King, Sea Lynx and Merlin helicopters, and ASV Maritime Defender, CASA-212 Patrullero, F-27, F-50, Harrier, Nimrod and P-3 Orion aircraft.
    In July 1996 the UK Ministry of Defence awarded the Underwater Weapons Division of GEC-Marconi (later Marconi Electronic Systems, now BAE Systems) a contract for the Full Development and Pre-Production (FDPP) phase of the Sting Ray lightweight torpedo life extension and capability update. The programme, against SR(SA) 7589, planned to bring current UK Royal Navy (RN) and Royal Air Force Mod 0 weapons up to an improved Mod 1 standard for a service life to 2020. In March 1997 UK MoD indicated that it intended to place a contract with BAE Systems Royal Ordnance for the life extension design, development and pre-production of a Mod 1 warhead assembly, to be based on the existing Mod 0 warhead. Between 1998 and 2001 A-model torpedoes were tested to prove the initial design work. This phase was followed by an evaluation of production-standard weapons in 2001 and 2002. The story of the Mod 1 upgrade has proved to be an extended one as the final contract was only signed by the UK Defence Procurement Agency (DPA) and the Underwater Systems Division of BAE Systems on 14 February 2003. The first plans for the programme dated back to 1988. The work will be undertaken in partnership with the Defence Munitions Depot, at Gosport. The first Mod 1 Sting Rays are planned for redelivery in 2006.

Description

Sting Ray is an advanced lightweight torpedo designed for launching from helicopters and fixed-wing aircraft as well as from surface ships. It is totally computer controlled; the software manages not only the acoustics and homing, but also the guidance and the tactics employed by the torpedo. This enables the weapon to select the optimum tactics to attack its target and also, should it miss, to reattack.
    Sting Ray is 2.6 m long, has a body diameter of 324 mm, weighs 265 kg and has a 40 kg Torpex shaped charge warhead. Its general shape and layout is relatively conventional and is made up of the following major assemblies:. Nose section, which contains the acoustic homing system, consisting of sonar transducers and transmitters, power electronics and receivers. The shaped charge warhead. Overall control is carried out in the guidance and control unit, where all the processing electronics are located, together with the target recognition facilities and the onboard computer. The seawater activated battery, which is sited close to the centre of gravity. The propulsion system and control surfaces. Finally, attached at the rear of the torpedo is the parachute pack to enable Sting Ray to be launched from a fast, high-flying aircraft, or a transiting or hovering helicopter. It also acts as a drogue when the torpedo is fired from deck-mounted tubes on a surface vessel.
    The homing system is designed to use the acoustic properties of seawater to its advantage and to acquire and home on to the modern, highly manoeuvrable and quiet submarines both in shallow water where sonar conditions are difficult and also in deep water. The acoustic output from, and input to, the torpedo is by means of a large number of electrically activated transducers in the nose. These, by suitable switching and multiplexing, can transmit high-power sound to the water or detect and receive the relatively low-power returns. Different shaped transmit beams or receive beams can be formed depending on the conditions and targets. In other words the transducers are used as a phased array to form and tilt beams as required. The heart of the torpedo guidance and control is its advanced digital computer, which controls both the propulsion and homing systems, and makes decisions on the necessary transmission and receive modes and attack modes. In doing so it uses both passive and active acoustic detection systems. In particular the active mode employs a frequency modulated transmission which can distinguish between real targets, rocks or countermeasures.
    The Sting Ray propulsion system has two contra-rotating propulsors housed in a duct forming a pump-jet system. Torpedo control is accomplished by an electro-hydraulically driven proportional control system, with four control surfaces mounted aft of the propulsor in the jet stream in order to give an early response during the critical phase on entering the water. The battery uses magnesium/silver chloride cells with seawater as the electrolyte, and is inert until the torpedo enters the water. Sting Ray employs a directed energy warhead required to counter modern submarine design. This type of warhead demands accurate guidance to ensure the torpedo strikes the most vulnerable part of the target.
    In operation, when the torpedo enters the water the parachute is discarded, and the battery, which rapidly fills up with seawater, comes up to power in 1.5 seconds and supplies electrical power to the electronic and propulsion systems. The computer carries out a height sense to determine water depth. If the water is shallow the torpedo runs at a fixed height contour following the bottom, rather like a cruise missile. Sting Ray then carries out a search pattern, the type depending on the operational situation, until the target has been acquired. The target is classified from the return signals and the torpedo closes on the target in approach homing. As the range closes, the torpedo measures, from the reflected sound waves, both the speed and aspect of the target. As a result, it calculates the correct course to not only bring it into collision with the target but to position it at the optimum point in order to enter the terminal homing phase. Finally the torpedo switches to terminal homing and hits the target at right angles to the hull in a preferred position to enable the warhead to be most effective. Sting Ray is believed to have a maximum speed of about 45 kt with an estimated endurance of some 8 minutes at that speed. Maximum operating depth is believed to be about 1 km.
    There are also exercise and dummy (handling, carriage and release) versions of Sting Ray. The exercise version is identical to the operational or warshot weapon, except that the warhead is replaced by a recovery and instrumentation section. This recovery and instrumentation section, which is made to the same weight as the warhead, carries a tracking system, a data recorder and a recovery unit. At the end of the run the torpedo is brought to the surface by means of a toroidal bag contained in the recovery and instrumentation section. The bag is inflated by a solid propellant hot gas generator.
    The Sting Ray upgrade programme will install Mod 1 modification kits into Mod 0 torpedo hulls. This involves the addition of several new 'front end' systems including a new digital sonar array, new guidance and control unit with an IMU, an auxiliary power unit, an enhanced signal-processing presetter, a new sea water battery, new motor controller electronics and a new electro-mechanical control system. The Sting Ray's warhead has been changed to a shaped charge insensitive munitions design of the same 40 kg weight, but with a new explosive composition. The 'back end' of the torpedo remains largely unchanged but does have a refurbished battery voltage regulator unit (to soft start the motor while the sea water battery is powering up) and some improvements to the safety and arming system.

Operational status

Sting Ray entered service in 1986. A production order for over 2,000 torpedoes for the UK was signed in 1986, and this was delivered by 1991. To date around 3,500 Sting Ray torpedoes have been built, and over 1,000 in-water runs have been undertaken both in development and operational usage, mainly against targets. Exports have been reported to Egypt, Norway and Thailand.
    Work on the Mod 1 upgrade programme for the UK is expected to begin in 2005 with the first upgraded Sting Rays redelivered to the Royal Navy and Royal Air Force in 2006. The Mod 1 will equip the RN's Lynx HMA.Mk 8 and Merlin HAS.Mk 1 helicopters and the Nimrod MR.Mk 2 (future MRA.Mk 4) patrol aircraft of the RAF.

Specifications

Length: 2.6 m
Body diameter: 324 mm
Launch weight: 265 kg
Warhead: 40 kg HE shaped charge
Guidance: Active/passive sonar homing
Propulsion: Electric pump jet
Range: n/k
Speed: 45 kt

Contractor

BAE Systems Underwater Systems Division