Tigerfish (torpedo)

The Mk 24 Tigerfish torpedo was a heavyweight acoustic homing torpedo used by the Royal Navy (RN) for several years. The early Mod0 and Mod1 variants were unreliable and unsuccessful, but were issued to the RN even though they failed Fleet Weapon Acceptance. Reliability was significantly improved in the Mod2 variant as a result of the Consolidation Programme which addressed the complete weapon system i.e. the on-board fire control system (TCSS10 and DCB) and the Mk24 torpedo. The Consolidation Programme was initiated following the torpedo's reliability failures during the Falklands War. It was headed by Marconi Underwater Systems Limited as Prime Contractor with Ferranti Computer Systems Ltd and Gresham Lion as major sub-contractors. Tigerfish was eventually replaced in-service by the much more capable Spearfish torpedo.

It was fitted with both active and passive sonar and could be remotely controlled through a thin wire which connected it to the launching submarine. Wire guidance permits a torpedo to be launched on-first-warning, i.e. when a target is first detected at long range. This permits the torpedo the time needed to close the range while target course and speed is being updated by the submarine's superior sensors and transmitted 'down-the-wire'. The torpedo can also be re-assigned to another target or recalled. Typically, wire-guided torpedoes initially run at low speed (in order to maximize their range and to minimize their self-generated noise) while they close the range (the approach speed) and speed up during the attack phase (the attack speed).

Design and development
The initial concept developed in the mid-1950s was for a very fast (55 knot/100 km/h), deep-diving torpedo driven by an internal combustion engine, carrying high pressure oxygen as oxidant, guided by a wire system developed from the Mackle wire-guidance study dated 1952 using data transmitted from the firing submarine sonars and using an autonomous active/passive sonar developed from the abandoned 1950s UK PENTANE torpedo project.

The weapon was known as Project ONGAR because Ongar railway station was, until 1994, the last on the Central Line of the London Underground system. The engineers developing this weapon were confident that it would be so advanced that it would be "...the end of the line for torpedo development".

The programme ran into serious problems in the late 1950s because the technology required was too advanced to meet an in-service target date of 1969. In addition, the closure of the Torpedo Experimental Establishment, Greenock, Scotland in 1959 and the transfer of its staff to Portland in Dorset disrupted the pace of development.

In the early 1960s a series of wide-ranging reviews (one report was titled "Whither ONGAR?" - the pun being intentional) led to a greatly reduced performance specification which was realistically expected to achieve an in-service date of 1969.

The propulsion system was changed from an internal combustion engine to an electric motor with a silver zinc battery as the power source. This reduced the planned speed of the weapon from 55 knots to 24 knots (100 km/h to 44 km/h) with a short final-attack-phase capability at 35 knots (64 km/h).

The homing system was simplified by the exclusion of the anti-surface ship capability in the Mod 0 weapon.

Only the wire-guidance system was retained relatively unchanged. This was similar to the system used on the earlier Mk 23 torpedo.

The original requirement for a crush depth of 1,000 ft (300 m) was overtaken by rapid advances in SSN deep-diving performance and the requirement was progressively increased to 1,600 ft (490 m) and then 2,000 ft (600 m). Tigerfish never met these requirements and the best that could be achieved was 1,150 ft (350 m) and later 1,450 ft (440 m); the structure was incapable of further crush-depth development.

In-service performance
Early models suffered from poor reliability: only 40% of the Mod 0 ASW model performed as designed. The torpedo depended in large part on the remote-control system, but the weapon tended to dip during launch, severing the control wire. The Mod 0 failed its initial fleet acceptance trials in 1979 but was nevertheless issued to the fleet in 1980. The Mod 1 DP (dual purpose) anti-submarine and anti-ship model also experienced problems, though a redesigned version (Mod 2) passed sea trials in 1978 and was issued the following year. When HMS Conqueror sank the ARA General Belgrano during the 1982 Falklands war she used the "point and shoot" 21" Mark VIII torpedoes rather than her Tigerfish. The Mark VIII had no homing system but, despite the design being over 50 years old at the time, was far more reliable and carried a greater high-explosive payload. In a test carried out by submarines returning to the UK after the war two of five Mod 1 Tigerfish fired at a target hulk failed to function at all and the remaining three failed to hit the target.

A measure of the Royal Navy's desperation for a reliable means of dealing with fast, deep-diving, time-urgent targets at long range resulted in a project to arm Tigerfish with a nuclear warhead to offset its poor diving depth and homing performance and to increase kill probability close to 90%. Various other measures were proposed in mid-1969, including purchase of U.S. weapons such as the Mark 45 ASTOR nuclear torpedo, the Mark 48 Mod-1 torpedo or the Subroc rocket. Alternatively, at the initiative of Flag Officer Submarines (FOSM), a nuclear warhead might be fitted to the unguided, shallow-running and short-ranged, but reliable Mark VIII torpedo. Flag Officer Submarines minuted that the proposal to arm the Mark VIII with the WE.177A warhead would, despite the torpedo's performance shortcomings, be "much superior to any present British submarine weapon ..." However, the short range of the Mark VIII put the firing submarine within damage range of the nuclear warhead of its torpedo.

The Marconi Consolidation Programme of the early 1980s finally produced the Mod 2 with reliability improved to 80%, which the Royal Navy accepted as the best that could be achieved with a basic design that was incapable of further development. By 1987 all 600 Tigerfish had been modified to the Mod 2 standard.

The tribulations with the Tigerfish torpedo development, from its concept in the mid-1950s to the introduction of the unsuccessful Mod 0 variant into Royal Navy service in 1980, were responsible for the decision to purchase cruise missiles to attack ships from Royal Navy submarines.

Versions were:
 * Mark 24-Mod-0 for ASW use. Dive depth 1,150 ft (350 m).
 * Mark 24-Mod-1 (or Mark 24 DP) for ASW and ASV use. Dive depth 1,450 ft (442 m).
 * Mark 24-Mod-1-N for ASW and ASV use. Dive depth 1,450 ft (440 m). The nuclear version - paper study only.
 * Mark 24-Mod-2 for ASW and ASV use. Dive depth 1,450 ft (440 m). The Marconi upgrade.

In 1990 Cardoen of Chile was granted a licence to manufacture Tigerfish for the Chilean, Brazilian and Venezuelan navies.

The Royal Navy retired the last of the Tigerfish torpedoes from service in February 2004.