48.Airborne Anti Submarine Warfare

(Published SP’s Special Supplement to Aero Inida 2015;19 Feb-21 Feb 2015)

Standoff antisubmarine capabilities continue to be of vital interest to the Navies across the world. The current environment of littoral warfare has once again brought in to sharp focus the threat of the lurking diesel submarine and the means of tackling it by the use of helicopters and aircraft. Some of the noteworthy anti submarine warfare platforms are discussed in brief in the succeeding paragraphs.

The Sikorsky CH-148 Cyclone is a twin-engine, multi-role shipboard helicopter being developed by the Sikorsky Aircraft Corporation. CH-148 is designed for shipboard operations and is intended to replace the CH-124 Sea King. It has a metal and composite airframe. A number of safety features such as flaw tolerance, bird strike capability, and engine burst containment have been incorporated into the design. It  is equipped to search and locate submarines during ASW. The Integrated Mission System and the Sonobuoy Acoustic Processing System are being developed by General Dynamics Canada. The sonar is an L-3 HELRAS, the radar is a Telephonics APS-143B, the Electro Optic System a Flir Systems SAFIRE III, and the ESM a Lockheed Martin AN/ALQ-210. CMC Electronics provides the flight management system CMA-2082MH Aircraft Management System. It carries 2 x MK-46 torpedoes on a bomb rack BRU-14 mounted in folding weapons pylons and a door-arm mounted general-purpose machine gun.

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The Agusta Westland AW101 is a medium-lift helicopter used in both military and civil applications. It has a digital automatic flight control system (AFCS) manufactured by Smiths Aerospace. This allows the operation of a four-axis (pitch, roll, yaw, and collective) autopilot and the automatic stabilization system, and is linked in with the aircraft’s flight management systems. The AFCS is a dual-duplex system using two flight computers to provide redundancy and fault-tolerance.

The AW101’s navigation system includes a GPS receiver and inertial navigation system, VHF Omni directional radio range (VOR), instrument landing system (ILS), Tactical air navigation system TACAN, and automatic direction finding. The Mk1 and Mk3 are equipped with a Doppler velocity system (DVS) which provides relative ground velocities; the DVS is also linked into the AFCS as part of the auto stabilization system. For safety, the aircraft is equipped with obstacle and terrain avoidance warning systems and traffic collision avoidance system (TCAS).

The AW101 is equipped with the Blue Kestrel search and detection radar, which is capable of 360 degree scanning and can detect small targets as far as 25 nautical miles. Royal Navy Merlins are equipped with the AQS901 anti-submarine system for processing sonographic data from sonobuoys to detect and target submerged submarines. Most variants of the AW101 are equipped with self-defense systems such as chaff and flare dispensers, directed infrared countermeasures (infrared jammers), ESM (electronic support measures in the form of RF heads), and a laser detection and warning system. Two hard points are present on the underside of the airframe on which it can carry four Sting Ray torpedoes or Mk 11 Mod 3 depth charges.

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The Airbus/Agusta Westland produced NH90 is designed to fulfill a NATO staff requirement for a multi-role, medium-sized military helicopter for both land and maritime operations. NH90 is the first helicopter in the world to be equipped with full fly-by-wire flight controls. NH90 is either fitted with Rolls-Royce Turbomeca RTM322 or General Electric T700E power plants.

The NH90 features a range of customizable avionics systems, dependent on customer selection and purpose. On some models, Thales Group provides various parts of the avionics, such as the glass cockpit, full-color multifunction displays, tactical mission and encrypted communication systems, the TopOwel helmet-mounted sight/display, IFF, and navigation systems, and the electrical power generation system. The naval NFH variant is outfitted with dipping sonar and sonobuoy processing equipment.

The Boeing P-8 Poseidon is a military aircraft developed for the United States Navy by Boeing Defense, Space & Security. The P-8 conducts anti-submarine warfare (ASW), anti-surface warfare (ASUW), and shipping interdiction, along with electronic signals intelligence (ELINT) role. The P8 can carry torpedoes, depth charges, SLAM-ER missiles, Harpoon anti-ship missiles, and other weapons. It is able to drop and monitor sonobuoys. It is designed to operate in conjunction with the Northrop Grumman MQ-4C Triton Broad Area Maritime Surveillance unmanned aerial vehicle.

ASW Armament

The ASW armament carried today by maritime aircraft and helicopters includes lightweight torpedoes, depth charges, and bombs.

Air Dropped Depth Charges and Bombs. Depth charges have again come into focus because of the ASW threat in littorals. These can be very effectively utilized for flushing out the lurking diesel submarines. Two depth charges are worthy of mention, these are the MK11 depth charge of UK and the BDC 204 depth charge of Sweden.

The Mk 11 depth charge was developed by British Aerospace (now BAE Systems) for air delivery from maritime aircraft and helicopters. The Mk 11 depth charge was designed for shallow water operations against submarines on the surface or at periscope depths. It is fully compatible for carriage and release from a wide range of ASW helicopters and fixed-wing maritime patrol aircraft. The Mod 3 version incorporates a 4 mm mild steel outer case and nose section, which is designed to withstand entry into the water at high velocities without distortion. It has been cleared for carriage on Lynx, Merlin, NH90, Sea King, and Wasp helicopters.

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The BDC 204 depth charge was developed by Bofors Underwater Systems (now Saab Dynamics) for air delivery from maritime aircraft and helicopters of the Swedish Navy. The depth charge can be deployed in patterns, with different depth charges set to detonate at different depths to achieve profound shock and damage to submarines. They have been cleared for carriage on the Boeing Vertol 107 helicopter and CASA C-212 Aviocar maritime patrol aircraft.

Air Launched Torpedoes. Few of the prominent air launched torpedoes are described below.

Stingray is a LWT manufactured by BAE Systems. It has a diameter of 324mm, weight of 267kg, and length of 2.6m. Its speed is 45kts with a range of 8km and its warhead is 45kg of Torpex. It can dive up to 800m.Stingray is fed with target data and other associated information prior to its launch, after entering water it searches for target autonomously in active mode and on acquiring the same, attacks it. It is carried by Nimrod aircraft. Stingray Mod1 is reported to have a shaped charge warhead and improved shallow water performance.

Mk46 Mod5 torpedo is the mainstay of US Navy’s air launched lightweight torpedoes. It is manufactured by Alliant Tech systems. It has a diameter of 324mm, length of 2.59m, with a weight of 231kg.It runs on Otto fuel, has a range of 11km with a speed of 40kts, and can dive upto365m. It has a PBXN-103 warhead of 44kg. It has an advanced digital computer control system with a built in logic and tactics for search and re-attack. It has effectively performed in both deep and shallow waters and can attack both the nuclear as well as the smaller diesel submarine. Over 25000 MK46 torpedoes have been supplied to customers until date. Interestingly the Chinese YU-7 torpedo is said to have been developed from the MK46 Mod2.

The Mk 54 Lightweight Torpedo is a hybrid of technologies taken from MK 46, MK48 and MK50 torpedoes. It is supposed to have homing and warhead of the MK50 and propulsion package of the MK46 torpedo. It has incorporated COTS processing technologies for an advanced guidance and control system. It is stated to have sophisticated shallow water capabilities for littoral threats. The MK54 torpedo has been finalized for P8i aircraft by India.

The A244/S developed by WAAS and currently manufactured by the Euro Torp consortium is a 324mm diameter, 2.8m long, and 244kg weight torpedo. It has a cruise/surge speed of 30/39kts, with a range of 6km and depth up to 600m. Its Homing head can function in mixed, active, or passive modes. It has special signal processing to distinguish target from decoys.

A244/S Mod.3 is the latest upgrade of the A244/S. It has more powerful propulsion battery, with an increased number of cells, which ensures a 50% increase in the endurance of the weapon to13.5 km. It has an Advanced Digital Signal Processor module to counter sophisticated torpedo countermeasures .The homing head has preformed multiple transmission and reception beams and multi-frequency operating capability. It can classify and track several targets simultaneously, and discriminate between the target and countermeasures.

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 MU90/Impact is in mass production for 6 major NATO and Allied Countries. The MU90/IMPACT torpedo is 323.7mm ‘NATO Standard’ caliber, 2.85 mm long with a weight of 304 kg. It is powered by an Aluminum-Silver Oxide seawater battery using dissolved sodium-dioxide powder as electrolyte with a closed-loop electrolyte re-circulation system, the torpedo is propelled by an electronically controlled high-RPM brush-less motor driving a skewed multi-blade pump jet propulsor allowing a continuously variable torpedo speed automatically selected by in built logic of the torpedo. The control and guidance electronics has embedded operational and tactical software including the signal processing, the data processing, and the torpedo guidance algorithms, which enable the MU90 to continuously self-adapt its configuration and tactics. The inertial system is based on ‘strap-down’ technology enabling all-attitudes capability including bottom following capability. The warhead consists of V350 explosive, fully insensitive, shaped charge warhead, with an impact type exploder incorporating two mechanical and six electrical independent safety devices.

 Low Cost Anti Submarine Weapon (CLAW) A200/A is a miniature torpedo developed by WASS. LCAW has been developed as an intermediary between air launched torpedoes and conventional depth charges. It is a low cost option, which provides propulsion and guidance to a depth charge without the costs of a torpedo. The air dropped version A200/A is deployed from aerial sonar buoy dispensers. The weapon is primarily designed to engage targets in shallow water, like midget submarines. The A200/A version has a length of 914.4mm, weight of 12kg, and a diameter of 123.8 mm. The warhead is a 2.5kg PBX shaped charge and the LCAW has an operating depth from 15m to300m. It has a speed of about 18kts with a range of 2km.

Indian Navy

The Indian Navy has ordered 8 in number of the P-8I Neptune version of the Boeing P-8 Poseidon. The aircraft includes six additional body fuel tanks for extended range from Marshall Aerospace; three of the tanks are located in the forward cargo compartment and three in the rear. In-flight refueling is via a receptacle on top of the forward fuselage, just aft of the cockpit. In order to power the additional electronics, the P-8 has an 180kVA electric generator. The P-8 uses data fusion software to combine its various sensors for target tracking.

The Bharat Electronics Limited (BEL) Data Link II communications allows the P-8I to exchange tactical data between Indian Navy aircraft, ships, and shore establishments. The P-8I features an integrated BEL-developed IFF system. India has purchased AGM-84L Harpoon Block II Missiles and Mk 54 All-Up-Round Lightweight Torpedoes for the P-8I. The Indian Navy inducted its first P-8I on 15 May 2013. The second and third P-8Is were received on 16 and 22 November 2013 respectively. In 2014, several Indian Navy P-8Is conducted search operations for the missing Malaysia Airlines Flight 370. The aircraft carries Raytheon APY-10 multi-mission surface search radar and is likely to have Advanced Airborne Sensor surface search radar and SIGINT package in the follow on program. It has 5 internal and 6 external stations for AGM-84H/K SLAM-ER, AGM-84 Harpoon, Mark 54 torpedo, missiles, mines, torpedoes, bombs, and a High Altitude Anti-Submarine Warfare Weapon system.

India’s Navy has selected Sikorsky Aircraft Corp., a subsidiary of United Technologies Corp. (NYSE:UTX), to fulfill the  Multi-Role Helicopter requirement for anti-submarine and anti-surface warfare (ASW/ASuW). Negotiations will now commence to procure 16 S-70B SEAHAWK helicopters, with an option for eight additional aircraft, along with a complete logistics support and training program. The Indian Navy S-70B variant will include avionics and flexible open architecture Weapons Management Systems that integrate advanced sonar, 360-degree search radar, modern air-to-surface missiles, and torpedoes for the ASW role. A blade and tail fold capability will facilitate shipboard storage.

Indian Navy has a requirement for 120 Helicopters (NMRH) in the 9-12.5 tons category. The NMRH is envisaged to carry out the ASW as well as the ASuW roles. Indian Navy is also interested in procuring 56 light utility helicopters for ASW and other support roles in the 4.5-ton class. In addition, there is a need to build an Indian Multirole Helicopter domestically in collaboration with HAL in the 12-ton class

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