Sting Ray torpedo

Sting Ray
HMS Westminster (F237) fires a Sting Ray Training Variant Torpedo from the tubes adjacent to her hangar
Type	Lightweight acoustic homing torpedo
Place of origin	United Kingdom
Service history
In service	1983–present
Used by	Royal Navy Royal Norwegian Navy Royal Thai Navy Romanian Navy
Production history
Designed	1969–80
Manufacturer	GEC-Marconi (Marconi Space and Defence Systems - MSDS), then Marconi Underwater Systems Ltd (MUSL) then BAE Systems Underwater Systems (part of BAE Systems Integrated System Technologies)
Specifications
Weight	267 kg (589 lb)
Length	2.6 m (8 ft 6 in)
Diameter	324 mm (12.8 in)
Maximum firing range	8–11 km (5.0–6.8 mi)
Warhead	Torpex
Warhead weight	45 kg (99 lb)
Engine	Electrical pump-jet Magnesium/silver-chloride batteries
Speed	45 knots (83 km/h)
Guidance system	Active and passive sonar
Launch platform	Frigates, destroyers, helicopters, and Nimrod aircraft

The Sting Ray torpedo is a current British acoustic homing light-weight torpedo (LWT) manufactured by GEC-Marconi, who were later bought out by BAE Systems. It entered service in 1983.

In the 1950s the Royal Navy was equipped with British designed and built Mk 30 air-dropped torpedoes. These were passive homing weapons which relied on detecting the noise from submarine targets. However, as submarine noise levels decreased these weapons became ineffective. A design for a British Mk 31 torpedo which would have used active echo-location sonar failed to receive Government approval for production. US Mk 44 torpedoes were purchased for the Royal Navy in the 1960s to fill this role, and later replaced by US Mk 46 torpedoes.

A desire to not be dependent on US torpedo purchases led to a research programme starting in 1964 to develop a British torpedo. Initially designated Naval and Air Staff Requirement (NASR) 7511, it was (much later in the late 1970s) designated the Sting Ray torpedo.

Design studies in the mid-1960s proposed that a tank of polyethylene oxide be carried behind the warhead. This polymer would be exuded at the nose to reduce the drag coefficient. Experiments using buoyancy-propelled torpedoes in 1969 had shown reductions in the drag coefficient up to 25%. However, by 1969 this scheme had been rejected in favour of carrying a larger battery.

The homing system developed in the mid-1960s incorporated a spinning magnetic disc onto which the acoustic correlation algorithms were etched but this was replaced by integrated circuit technology when the disc sometimes failed to survive the impact of the weapon with the sea from high altitude launches.

The original warhead concept was for a simple omnidirectional blast charge. However, studies in the 1970s showed that this would be inadequate against the large double-hulled submarines then entering service. A directed energy (shaped charge) warhead was used in the production weapon.