Airborne Anti-Submarine Warfare

Sikorsky Aircraft has been selected by the Indian Navy to fulfil its multi-role helicopter requirement for anti-submarine and anti-surface warfare missions

Issue: 3 / 2015By Rear Admiral Dr S. Kulshrestha (Retd)Photo(s): By BAE Systems, US Navy

Standoff anti-submarine 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 (ASW) platforms are discussed in brief in the succeeding paragraphs.

Sikorsky CH-148 Cyclone

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 is equipped to search and locate submarines during ASW. The Integrated Mission System and the Sonobuoy Acoustic Processing System are being developed by the 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.

Sikorsky S-70B Seahawk

Sikorsky Aircraft has been selected by the Indian Navy to fulfil its multi-role helicopter requirement for ASW and anti-surface warfare (ASuW) missions. The current requirement projected is 16 with an option from additional 8. It has been developed from the US Army’s UH-60A Black Hawk. The SH-60B carries a complex system of sensors including a towed magnetic anomaly detector and air-launched sonobuoys. Other sensors include the APS-124 search radar, ALQ-142 ESM system and optional nose-mounted forward looking infrared turret. It carries the MK-46, MK-50, or MK-54 torpedo, AGM-114 Hellfire missile, and a single cabin-door-mounted M60D/M240 7.62mm (0.30 in) machine gun or GAU-16 .50 in (12.7mm) machine gun. The Indian Navy’s S-70B variant is expected to feature avionics and flexible, open architecture weapons management systems, which are equipped with an advanced sonar, 360-degree search radar, modern air-to-surface missiles and torpedoes for ASW missions.

AgustaWestland AW101

The AgustaWestland AW101 is a medium-lift helicopter used in both military and civil applications. The AW101’s navigation system includes a GPS receiver and inertial navigation system, VHF Omni directional radio range, instrument landing system, tactical air navigation system and automatic direction finding. For safety, the aircraft is equipped with obstacle and terrain avoidance warning systems and traffic collision avoidance system. 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. Most variants of the AW101 are equipped with self-defence systems. 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.

Depth charges have again come into focus because of the ASW threat in littorals. These can be very effectively utilised for flushing out the lurking diesel submarines.

NH90

The Airbus/AgustaWestland produced NH90 is designed to fulfil 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 customisable avionics systems, dependent on customer selection and purpose. The naval variant is outfitted with dipping sonar and sonobuoy processing equipment.

Boeing P-8 Poseidon

The Boeing P-8 Poseidon is a military aircraft developed for the US Navy by Boeing Defense, Space and Security. The P-8 conducts ASW, ASuW and shipping interdiction, along with electronic signals intelligence role. The P-8 can carry torpedoes, depth charges, SLAM-ER missiles, Harpoon anti-ship missiles, and other weapons. It is able to drop and monitor sonobuoys. Indian Navy has acquired eight P-8I which have been adapted as per India’s operational requirement.

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 utilised for flushing out the lurking diesel submarines. Two depth charges are worthy of mention, these are the MK-11 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 4mm 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.

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 267 kg, and length of 2.6 metres. Its speed is 45 knots with a range of 8 km and its warhead is 45 kg of Torpex. It can dive up to 800 metres. 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 Mod 1 is reported to have a shaped charge warhead and improved shallow water performance.

MK-46 Mod 5 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 2.59 metres, with a weight of 231 kg. It runs on Otto fuel, has a range of 11 km with a speed of 40 kts, and can dive up to 365 metres. It has a PBXN-103 warhead of 44 kg. 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 the nuclear as well as the smaller diesel submarine. Over 25,000 MK-46 torpedoes have been supplied to customers until date. Interestingly the Chinese YU-7 torpedo is said to have been developed from the MK-46 Mod 2.

The MK-54 lightweight torpedo is a hybrid of technologies taken from MK-46, MK-48 and MK-50 torpedoes. It is supposed to have homing and warhead of the MK-50 and propulsion package of the MK-46 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 MK-54 torpedo has been finalised for P-8I aircraft by India.

The A244/S developed by WAAS and currently manufactured by the Euro Torp consortium is a 324mm-diameter, 2.8-metre-long, and 244-kg weight torpedo. It has a cruise/surge speed of 30/39 knots, with a range of 6 km and depth up to 600 metres. 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 per cent increase in the endurance of the weapon to 13.5 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.

MU90/Impact is in mass production for 6 major NATO and allied countries. The MU90/Impact torpedo is 323.7mm NATO Standard calibre, 2.85mm long with a weight of 304 kg. It is powered by an aluminium-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 brushless 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 (LCAW) 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 sonarbuoy 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 12 kg, and a diameter of 123.8mm. The warhead is a 2.5 kg PBX shaped charge and the LCAW has an operating depth from 15 metres to 300 metres. It has a speed of about 18 knots with a range of 2 km.

Indian Navy

The Indian Navy has ordered eight 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. In-flight refuelling 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 180 kVA electric generator. The P-8 uses data fusion software to combine its various sensors for target tracking.

The Bharat Electronics Limited 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 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 programme. It has five internal and six 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. Six have been delivered and remaining two will be delivered this year.

IN has selected Sikorsky Aircraft Corp., a subsidiary of United Technologies Corp, to fulfil the multi-role helicopter requirement for 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 programme. IN has a requirement for 120 NMRH in the 9-12.5 tonnes category. The NMRH is envisaged to carry out the ASW as well as the ASuW roles.