SST-721 torpedo

SST-721 Torpedo
SST-721 Torpedo.fw.png
TypeHeavyweight torpedo
Place of origin Carthage
Service history
In service2004–present
Used byCarthage Carthage
GensokyoRepublicFlag.png Gensokyo Republic
Production history
DesignerAcheron Technologies
ManufacturerAcheron Technologies
Unit costNSD$3.8 million
No. built6,900
VariantsMark 2 Rev. 3
Specifications (Mark 2 Rev. 3)
Weight3,150 kg (6,940 lb)
Length8.86 m (29.1 ft)
Diameter660 mm (26 in)

Effective firing range50 km (27 nmi) @ 75 kn (139 km/h)
90 km (49 nmi) @ 40 kn (74 km/h)
150 km (81 nmi) @ 25 kn (46 km/h)
WarheadAluminised PBX explosive
Warhead weight450 kg (990 lb)
Proximity or contact

EngineIntegrated motor propulsor
PropellantAl-AgO battery (120 kWh)
Speed75 knots max

The SST-721 Master Spark is a heavyweight submarine-launched torpedo in service with the Punic Navy. Introduced in 2004, it replaces the previous Type-27 heavyweight torpedo as the primary armament for Carthaginian submarines. With its large warhead, long range, and quiet propulsion, the Master Spark is designed primarily for use against large surface targets such as aircraft carriers, stand-off attacks against predictable targets like merchant convoys, and for ambush use against targets where extreme stealth is required.


The 660 mm Type-27 battery-powered heavyweight torpedo was introduced in 1977 as a supplement to the swashplate-powered Type-24 following the Northern War in order to address perceived deficiencies in Type-24 field performance. While slower than the Type-24, the Type-27 was significantly quieter, allowing for improvements in detection against very quiet diesel-electric submarines. In addition, the switch to battery power allowed the Type-27 to outperform the Type-24 at greater depths where the pressure required to expel exhaust gases from the Otto-fueled engine required significant power to be diverted from propulsion. The Type-27 performed according to expectations in design trials, but limited range and speed prevented the type from completely replacing the Type-24.

In 1986, the Type-27 Mark 2 was introduced, improving motor performance and closing the gap between the thermal-powered Type-24 Mark 3 and the electric Type-27. As a result, the Type-24 was slated for retirement, with final replacement of Type-24s in active service occurring in 1991. Type-24s were retained in reserve inventory for use in training and for possible export, and all unsold inventory was dismantled by 2003. While initially slated to replace all other heavyweight torpedoes in service, the Type-27 was supplemented by the "short" Type-28 turbine-powered torpedo to alleviate concerns about weapon storage capacity.

Despite closing the gap in performance versus legacy torpedoes, concerns were raised in the mid-1990s regarding the survivability of Carthaginian submarines using the Type-27 and its suitability against increasingly stealthy submarines. In addition, the current inventory of torpedoes was expected to reach the end of their shelf lives beginning in 1998, requiring either replacement or refurbishment of the same type or a new design. In 1999, the Punic Navy initiated the Torpedo 21 project to develop new heavy and lightweight torpedoes to replace the Type-27 and lightweight Type-35. Requirements specified improved range and sensitivity and reduced lifecycle costs while maintaining compatibility with existing launch systems.

The contract was issued to Cyrene-based Acheron Technologies in December 1999. The award was hotly contested among competing suppliers, in particular the RMA Corporation, over perceived unfairness in the bidding process and the nature of the competition's subcontracting requirements. Due to mounting setbacks and delays in the program, a refurbishment program to inspect and certify existing stockpiles for extended service was initiated, with the refurbishment contract awarded in a separate bidding system.

First trials of the new SST-721 torpedo took place in mid-2003, with low rate initial production beginning in 2004. Full-rate production was scheduled for 2006 but was delayed due to deficiencies with the onboard software and motor-propulsor. Modifications to the design pushed full-rate production to January 2009, with the improved Mark 2 Revision 3 model. The SST-721 is expected to replace all stocks of the Type-27 in active service. An estimated 56,000-60,000 torpedoes are expected to be procured throughout the life of the program.



The Master Spark is capable of operating in both wire-guided and self-guided acoustic search patterns, as well as a wake-homing mode for use against surface ships. When launched, the SST-721 trails a fiber-optic cable for remote guidance. Digital signal processing and guidance elements allow additional situational data to be downlinked to the torpedo, including sea state information and target characteristics, enabling the torpedo to better accommodate such factors in course plotting. Additional space for modular guidance upgrades is available, although at present 80% of the SST-721's computing capacity is unused.

A highly accurate ultra-broadband beamforming sonar is used to improve target discrimination over previous generation torpedoes. The transducer array is composed of some 290 elements in a 18 x 18 array and can track and classify over 150 underwater targets, screening out decoys and non-targets in cluttered littoral waters. The sensitivity of the system has also been greatly improved thanks to the isolation of the motor and other improvements in hydrodynamic flow, allowing for reduced ambient noise. Estimates place detection range improvements at over 200% versus the Type-27.

In combat the torpedo is reported to act in a multi-speed profile depending on target range and speed. Close-range targets are generally engaged with a high run-out and transit speed followed by a lower speed to reduce flow noise to allow the torpedo to acquire its target. Once acquired, the torpedo may again return to high-speed operation as the target magnitude grows stronger.

As the torpedo's maximum range exceeds the practicable length of any wire guidance system, when used against distant targets the SST-721 is equipped with a deployable satellite navigation and communications antenna. When raised, the torpedo can receive position updates and mid-course guidance instructions from aircraft or satellites, enabling it to accurately track targets beyond the range if its wire guidance system.


The SST-721 uses the same warhead as the Type-27 Mark 2, a 450 kg (1,000 lb) aluminised PBX shaped charge designed to breach the thick pressure hulls of deep-diving submarines as well as surface ships. Warheads deployed to fleet torpedoes are a mix of both new and refurbished warheads from retired Type-27s converted to training usage with a newer, more reliable fuze rated for longer lifetime between inspections.

The warhead may be triggered by an onboard magnetic sensor, active sonar, and impact fuzing. While tethered, the torpedo may also be remotely detonated should it become a hazard to friendly ships or fail to acquire a target.

Although not currently deployed in any active configurations, the SST-721 is also capable of accepting the R-47 nuclear warhead also designed for the Type-27, with a 10 kiloton yield.


Like the Type-27, the Master Spark uses batteries for propulsion, but introduces more advanced aluminum-silver oxide batteries. The higher power density allows for a higher maximum speed and greater endurance, increasing the submarine's engagement envelope. As with other battery powered torpedoes, the SST-721 is capable of operating at extremely deep depths without a loss in performance compared to swashplate or turbine powered engines, as there is no need to expel exhaust products against the ocean pressure. The maximum operating depth is believed to be in excess of 1,000 metres (3,300 ft), allowing the SST-721 to engage deep-diving and bottomed submarines.

The SST-721 adopts a contrarotating rim-driven integrated motor-propulsor like the Type-06X family of submarines, allowing the motor to be housed in the propulsor housing. This decouples the motor from the torpedo body itself, increasing available space for batteries as well as allowing for improved acoustic isolation of the motor from the bow sonar. The use of an electric motor in combination with a battery bank provides greater flexibility in speed without a loss in efficiency, providing the SST-721's prodigious low-speed cruising range.

A training variant is in development, expected to use conventional rechargeable batteries to make the torpedo fully reusable. In the interim, training is conducted using Type-27T training torpedoes, which are dimensionally identical and have similar handling and servicing procedures.


See also

Related development

Related lists

Comparable torpedoes