The sinking of the Republic of Korea Navy corvette Cheonan in March 2010 provided a stark reminder of the destructive power wielded by the heavyweight torpedo, fired from a single diesel submarine in the hands of a competent crew, and their ability to cripple or destroy a mission essential unit. The incident was also a re-affirmation to navies worldwide of the requirement for an effective anti-submarine warfare (ASW) capability that includes robust torpedo defence.
During the decades since World War II and The Cold War, a large number of regional navies have pursued the acquisition of modern, extremely quiet diesel-electric submarines equipped with state-of-the art command, fire control and sonar systems and advanced heavy weight torpedoes. In a potential enemy's hands, these submarines present a significant risk to surface forces and/or logistics shipping passing through chokepoints, and a similar threat to the freedom of manoeuvre in littoral areas.
In response navies are today investing in Surface Ship Torpedo Defence (SSTD) systems to effect protection for their valuable naval units. One such system is Ultra Electronics' Sea Sentor, the SSTD market leader. Ultra's Sea Sentor variant, Sonar 2170 for the Royal Navy, is the only operational Torpedo Defence System that detects, classifies by type, locates and provides specific countermeasures against heavyweight torpedoes. At the heart of the Sea Sentor system is the passive Torpedo Detection, Classification & Localisation (TDCL) software, this software is now being further developed to provide an active DCL to combat the increasing threat from ever quieter electric torpedoes. Other developments include the provision of lighter weight arrays for smaller vessels, integration of sonobuoys into the deployable sensor mix, Force Torpedo Defence planning aids and the modification of the system for Submarine Torpedo Defence systems.
System innovation
Sea Sentor is a compact, modular and self-contained system that integrates advanced TDCL techniques with a suite of soft-kill countermeasures (comprising both off-board expendable devices and towed decoy).
In operation, Sea Sentor detects active and passive homing torpedoes, including wake homers, at sufficient range to enable the deployment of acoustic countermeasures to maximise the probability of vessel survivability. It uses a dedicated, passive digital array and intercept towed sensor to achieve detection; this sensor is normally deployed to a depth below the surface layer, so providing for a significantly greater detection range over a hull-mounted sonar and beyond torpedo firing range.
Automatic TDCL functionality is hosted on COTS processing technology located within the Sea Sentor electronics cabinet. Associated threat evaluation software provides full torpedo and countermeasure manoeuvre and action to the command, and automatically initiates countermeasures actions relevant to the specific threat. Expendable acoustic countermeasures, designed to seduce incoming torpedoes away from the host ship, are launched from eight-barrel fixed launchers, mounted port and starboard. An in-line flexible towed acoustic body, streamed behind the vessel, incorporates a multi-mode countermeasure device. Control and display equipment is designed to occupy a minimal footprint. A launcher control unit and heads-up display panel are fitted in the operations room with an additional heads-up repeater display on the bridge.
SSTD - Engineered for future growth
The Sea Sentor system has been engineered to accommodate further capability growth in order to counter future threats with an Active TDCL in development. In addition, the processing rack has significant space for expansion; the towed assembly is able to accommodate additional sensors and is one module of the Integrated Sonar System (ISS) assembly currently being provided to the Australian Air Warfare Destroyer programme. The SSTD launcher system is expandable and capable of launching alternative countermeasure payloads. Alternative countermeasures concepts, including a hard-kill option may also be incorporated into the overall system.
Furthermore, Sea Sentor differs from earlier generation and a number of current generation torpedo defence systems in that it acts as a force sensor able to detect threats and provide early warning to other non-SSTD fitted vessels within a task group. Building on this capability, Ultra is now pursuing the development of a command planning tool for the control and de-confliction of force-wide reactive torpedo defence.
This software-based planning module will apply embedded real-time operational tactics to manage the optimisation of the force-level SSTD posture and response as dictated by the threat scenario. This tool will provide a means for the force commander to automate the co-ordination and execution of area-wide undersea defence operations through optimal use of defensive assets, a higher degree of force collaboration and rapid situational understanding.
It would also have applications as an off-line planning tool, enabling operational staffs to develop methodical and synchronised plans designed to de-conflict unit reactions, reduce response times and minimise the damage to defended high-value assets. In addition, the same module could, as a matter of routine, support the deployment of the Sea Sentor sensor for intelligence gathering purposes in regional areas of interest.
Sea Sentor systems have been sold to the Turkish Navy for their Milgem Class Corvettes and negotiations are underway with at least five other allied nations for the delivery of this system for both new build and existing classes of warships and auxiliaries. The Sea Sentor software has been further developed for Submarine Torpedo Defence systems and is currently being adapted for the Turkish Navy for their new build 214 Class Submarines.
A force-level SSTD capability could also benefit from advances in sensor and effector technology already being explored by Ultra. For example, the company is investing private venture funds in the demonstration of an Active Torpedo Detection capability that would enable reliable detection, at tactically significant ranges, of future quiet torpedo threats expected to enter service in the 2015 - 2020 timeframe. Ultra has also demonstrated mobile acoustic countermeasures which offer expanded options to the command, particularly in situations where manoeuvre space is limited.
In summary, Sea Sentor will detect an incoming torpedo and classify to type using the threat database. The system will then automatically alert the operator and activate the towed countermeasure. At the same time the system assesses appropriate manoeuvres for the vessel to take and alerts the operator to which countermeasures should be launched, from where (Port or Starboard launchers) and when. This combination of towed countermeasures, ship manoeuvre and expendable countermeasure launch pattern is designed to give the ship the highest probability of evading and countering the particular type of incoming torpedo. This "sensor-to-countermeasure" capability is unique to Ultra Electronics Sea Sentor System.
