24. Hovering Danger- Guided Weapons of Naval Helicopters

(Published in SP’s Naval Forces, Jun-Jul 2013)

Hovering Danger- Guided Weapons of Naval Helicopters

The first helicopter to be widely used in the US and the UK navies was the Sikorsky R-4, powered by a radial engine to rotate its main rotor with three blades. Interestingly the earliest use of the R-4/R-5 helicopter was as a ‘plane guard’ to recover pilots in case they ditched near the aircraft carriers. In fact the US Navy at one time opined that the helicopter would never be big enough for useful deployment at sea by the Navy! Today with advancement in technology, the Naval Helicopters are assigned the tasks of; Anti submarine Warfare (ASW), Combat Search and Rescue (SAR), anti ship surveillance and targeting (ASuW), Mine warfare countermeasures (MCM), surveillance, reconnaissance and target acquisition, over the horizon targeting, electronic countermeasures (ECM), communication relay, Naval surface fire support (NSFS), ship boarding and Utility. In fact the capabilities and sub capabilities of the SH-60 helicopter with the US Navy additionally include; Amphibious Warfare, Anti Air warfare, Electronic warfare, Fleet support operations; Command, control and communications etc.

The development of the Naval Helicopter today, owes its lineage to its primary development in an anti submarine role to combat enemy submarines. The US Navy visualised the role of the Naval Helicopter in combating the German Submarines which were threatening US as well as allied shipping. It was envisaged that Coast Guard pilots would fly the helicopters to guard the convoys by scouting for submarines and operate from the platforms on decks of merchant ships. The first Sikorsky R-4 Naval helicopter was inducted in 1943. Thereafter it began the trials for ‘Evaluation of the Ship Based Helicopter in Anti-Submarine Warfare’. In the anti submarine role it was thought that once the sonar of a destroyer detected a submarine the Helicopter would be guided to the submarines location and would drop a MK IX 200-pound depth charge, thereafter it would be replenished from the destroyer. In 1944, trials were carried out to fit the helicopter with dipping sonar, to  make it more autonomous, the fears of excessive noise due to rotors and downward wash proved to be unfounded, further, as a spin off it was observed that helicopters were very useful in alignment of fire control and anti aircraft radars. Thereafter in the late fifties ASW helicopters were equipped with light weight torpedoes and they were extensively used to track and detect nuclear submarines. The Sea King and the LAMPS followed, the current version SH-60 R has upgraded avionics, multimode radar, advanced low frequency sonar, guns, missiles and torpedoes for combating targets in the littoral regions.

Indian Navy has a requirement for both multi role as well as light utility helicopters, to replace its aging Sea Kings and Chetaks. The Multi Role helicopter procurement is at commercial bid opening stage, with two contenders namely Augusta Westland NH-90 and Sikorsky S-70B. Indian Navy has also issued an RFI for 120 Helicopters (NMRH) in the 9-12.5 tons category and RFP is likely in a couple of months. The NMRH is envisaged to carry out the ASW as well as the ASuW roles. Indian Navy has also issued an RFP for 56 light utility helicopters for ASW and other support roles.

The essential weapons on board the Naval helicopters are the aerial torpedo (Light weight Torpedo, LWT) and the anti shipping missiles, therefore it would be worthwhile to look at few prominent weapons in these categories.

Helicopter Launched Aerial Torpedoes

The aerial torpedoes were extensively used in the WW II; however, it is a fact that with the advent of the cruise missile the torpedo has been confined to its role against submerged submarines only. The anti shipping missiles have longer range, much higher speeds and easier deployment than the aerial torpedoes and therefore they are preferred for the anti shipping role.

A244 S Mod 3 is an upgrade of the A 244S from WASS Italy. The main improvements include an acoustic seeker which has pre-formed multiple transmission and reception beams and multi-frequency operating capability. This ensures high performance in very shallow waters and at very long engagement distances. The warhead is Omni-directional type which is designed to maximise the lethal effect. Simultaneous classification and tracking of several targets is possible due to its advanced Digital Signal Processor, which is also able to clearly discriminate between the real and false targets. The battery package has increased number of cells which gives the Mod 3 an increase of about 50% in range. It also features a D-C contra rotating motor with an electronic controller for variable speed propulsion. The main features of its homing head include; active homing ranges greater than 2100 m, very low TS acquisition capability, Narrow and broad band modes, Active /passive modes, capability to detect bottomed targets, classification based upon spatial diversity, multi frequency, and signal processing. Its low noise and programmable acoustic enabling delays detection by the target ship of the oncoming torpedo. With a length of 2.75 m, weight of 250 Kg it has a maximum speed of 38 kts and an endurance of 13500 m/10000 m depending upon low/high speed.

The MU90/IMPACT marketed by the consortium EUROTORP is the main NATO torpedo and is considered to be the most advanced LWT. It weighs 304 Kg and has length of 3.237 m. It is claimed that pre-arrangements to cope with Submarine-Launched Anti-Air-Missile (SLAAM) have already been incorporated in the system. It can operate between depths of 25 m to 1000 m and is navigable up to 3 m. It is claimed that its multi-frequency, parallel processing and simultaneous acoustic modes operation, allow multi-target tracking capability, and provides the weapon with immunity against anti-torpedo countermeasures. The strap down control and guidance capability allows it to manoeuvre in all attitudes. It has an engagement range of 15000 m. The warhead is STAGNAG compliant V350 insensitive shaped charge with an impact exploder. The safeties include two mechanical and six independent electrical devices.

 The MK 54 by Raytheon incorporates the best of technologies from MK 50, MK 48 ADCAP and MK 46 torpedoes. The acoustic head, an upgrade from MK 50, provides low self-noise and superior  performance in littoral areas. Control and guidance is a combination of features from MK 48 and MK 50 with the latest commercial-off-the-shelf (COTS) processing power (14 gigaflops) in an expandable open architecture. The warhead consists of the MK 103 Mod 1 Warhead and the MK 20 Mod 0 Exploder.

 The Flash Black from WASS, currently under development, is claimed to have features of the next generation of LWTs. The design of the Flash Black is highly versatile with the capability to be launched from multiple platforms (underwater and AUV, UUV and USV), against any target and in any environment, including littoral waters and in extremely shallow depths. It can counter even the most sophisticated countermeasures.

Helicopter Launched Anti Ship Missiles

 The major role of the Naval Helicopter in an anti ship operation is that of the Over the Horizon Targeting (OTH) of anti ship cruise missiles (ASCM). This requires that target vessel be acquired, tracked and the data passed on to the main ship and/or carry out mid course and terminal guidance of the launched ASCM. The Naval helicopter is generally armed with lighter missiles capable of destroying smaller craft and crippling larger ships, it provides protection to own ship against patrol boats; fast attack crafts etc. and supports the launch ship against larger enemy ships.

 The AS.12 anti ship missile was inducted in the French Navy in 1960 for attacking ships and submarines on the surface. It had a bulging nose and four clipped triangular wings. It functioned with two solid fuel rocket motors; a powerful booster rocket that burned for 2.2 seconds and a sustainer motor that burned for 28 seconds. The missile guidance was by using four metal vanes around the exhaust nozzle in a thrust vectoring system, the steering signals were sent to the missile by means of two wires which were paid out from two spools on the rear of the missile. A gas operated arming mechanism fed from the sustainer motor, armed the warhead 7.7 seconds after launch. The weight of the warhead was 28 kg.

The Penguin was the first NATO anti ship missile with an infra red seeker developed in collaboration between the Kongsberg Våpenfabrikk and Norwegian Defence Research Establishment, with financial support from West Germany and USA. It entered service in 1972. It could be fired from a number of helicopters like SH 60 Seahawk and Westland Super Lynx. The missile was inertial guided until the autonomous terminal phase. It had a solid rocket engine and a 120 kg warhead.

Another light weight anti ship missile for deployment form the Lynx helicopter is the British Sea Skua, which has a blast fragmentation SAP warhead of 28 kg. It can travel at one of the four preselected heights based upon the prevailing sea surface conditions; it climbs up as it nears the target to acquire it. The Missile homes on to the target illuminated by the helicopters radar.

Marte MK 2/S is an anti-ship missile by MBDA which is fully qualified on helicopter AW 101. The Marte MK 2/S is the technologically advanced version of Marte MK 2 of the Italian Navy’s SH3D helicopter fleet. It has a weight of 310 kg, length of 3.85 m. It is a high subsonic missile with a range of 30 km. Marte  ER is the advanced version of the Marte series, while it retains the existing features like the sea skimming capability, all weather operation and the radar homing head, it has an extended range of over 100 km. The longer range is the result of incorporating a turbo jet engine. This, along with advanced avionics enable the missile to have multiple selectable trajectories and flight profiles, an option for in-flight target re-vectoring is also available. High subsonic speed, ECCM, inertial and GPS navigation would make it a formidable weapon in both littoral as well as high sea environment. It would be fully interoperable with the MK 2/S version.

 DELILAH HL, this missile for the helicopter launch has been developed by Israel Military Industries (IMI) from its successful DELILAH missile. It offers new offensive capabilities for attacking targets in coastal, littoral, blue waters and on land. With a range of over 250 km it allows the helicopter to remain outside the range of long and medium range SAMs as well as the air defence systems of the enemy ship. The missile has a weight of 230 kg, with a length of 3.20 m. It has INS/GPS navigation with a data link for target validation. The warhead weight is 30 kg and it has speeds between Mach 0.3 – 0.7.

 The Exocet AM 39 is the air launched version of the Exocet missile family, and a product of MBDA. The missile weighs 670 kg, it is 4.6 m long and it flies at a speed of 315 m/sec. It has a solid propellant engine, with a booster and a sustainer, and a range of 70 km. Its warhead is 165 kg of insensitive explosive, optimised for HE blast and pre-fragmented effects, with impact fuse and proximity function. It is an inertial guided missile with active radar homing for the end phase. It flies very close to the sea surface (≤ 2m) which gives very little reaction time to the target. It is a battle proven missile.

 Future Trends

Developments in the unmanned rotary craft technology has opened entirely new vistas to weapon designers who are taking inspiration from mini weapons developed for UAVs for incorporation in to the unmanned helicopters. An example of the unmanned helicopter is the MQ 8B Sea Scout, the marinised version of the MQ 8B Fire Scout, being developed by Northrop Grumman for the US Navy. The Sea Scout would be fitted with an Advanced Precision Kill Weapon System which is a laser guided 70 mm rocket. In addition the US navy has asked that RDR-1700 Surveillance Radar be mounted underneath the Sea Scout; this synthetic aperture radar can look through sandstorms and clouds and can track 20 air/ surface targets.

 The transition from the naval helicopter to the smaller and lighter unmanned naval helicopter appears to be certainty (at least partially), which would ensure availability of these unmanned craft on much larger number of smaller ships. This would lead to rapid development of associated weapons, like micro miniaturised missiles and ultra light weight torpedoes, which could relieve the ship of targeting smaller craft and midget submarines in the littoral environment.