Weapons: Cruise missiles for the ADF | ADM July 2009

Julian Kerr | Sydney

The possible acquisition of such a long-range land attack capability has for years been a sensitive political issue, particularly with Indonesia; one which has militated against any move to retrofit the Collins class submarines with Tomahawk.

Now, however, the Rudd government has announced its intention to deploy land attack cruise missiles not only on the Future Submarine that will replace the Collins class but also on the eight Future Frigates that will eventually supercede the Anzac class, and, of more immediate interest, on the RAN's three air warfare destroyers (AWDs).

The White Paper refers to the necessary control and firing systems being fitted to the AWDs as "an early enhancement".

In practical terms, there seems no reason why the capability should not be available from the time the first AWD is handed over to Navy in 2014.

The integration process stands to benefit from Spain's decision to become the third Tomahawk user after the US Navy (USN) and Britain's Royal Navy (RN) and deploy Block IV missiles on its five F-100 frigates, the class on which the design of the RAN's AWDs is based.

During the first five years of service, this technology cannot be used by the Spanish Navy without US permission - a constraint which Australia would seem unlikely to face, or to accept.

The BGM109E is an all-weather submarine or ship-launched land attack missile with a range of about 2,000 kilometres and a 450 kg unitary warhead.

Powered by a Williams International F107-WR-42 turbofan engine, the 1,440 kg missile is designed to fly at extremely low altitudes at a speed of up to 880 kilometres an hour.

The missile's small radar cross-section and low altitude flight make radar detection difficult, while infrared detection is unlikely because of the small heat output from the turbofan engine.

The Tomahawk Weapon System (TWS) comprises four major components - Tomahawk missile, theatre mission planning centre, Tactical Tomahawk weapons control system (TTWCS) for surface ships, and combat control system for submarines.

The fire control systems on both ships and submarines perform database management, engagement planning, and launch control functions.

Critically, they also support bi-directional communication between the launch platform and the missile.

Aboard launch platforms, the TTWCS prepares and executes the launch by identifying the appropriate missile, applying power, transferring alignment and mission data, and firing the missile.

During preparation, the operator establishes way-points to create the over-water portion of the route.

Launching and guidance
Shipboard missiles are stored and launched in the Mk 41 vertical launch system (VLS).

Most submarine-deployed Tomahawks are launched from torpedo tubes (with stowage in the torpedo room), although some utilise a VLS located forward, external to the pressure hull, to handle both stowage and launch.

The missile utilises a solid propellent rocket motor to accelerate the missile through the initial boost phase of flight until the turbofan engine takes over.

Over water, the Tomahawk uses inertial guidance or GPS to follow a preset course; once over land, the missile's guidance system is aided by Terrain Contour Matching (TERCOM).

The TERCOM radar uses a stored map reference to compare with the actual terrain to determine the missile's position.

If necessary, a course correction is then made to direct the missile to the target.

Terminal guidance in the target area is provided by the optical Digital Scene Matching Area Correlation system, which compares a stored image of target with the actual target image.

This produces a claimed accuracy of about 10 metres.

Tomahawk was first introduced by General Dynamics in the 1970s and now, numerous iterations later, is manufactured by Raytheon.

Also known as the Tactical Tomahawk, the Block IV variant provides a range significantly beyond the 1,800 km of the Block III, and includes a two-way ultra high frequency satellite communication link.

This allows the strike controller to flex the missile in flight to engage up to 15 pre-programmed alternative targets, abort the mission, or redirect the missile to a new destination.

This targeting flexibility includes the ability to loiter over the battlefield awaiting an assignment to a time-critical target.

The missile can also use the satellite data link to transmit missile health and status messages, as well as battle damage indication imagery just before it impacts on the target.

Current capability
Limited maritime-based land attack capability out to a range of about 124km is already available to the ADF in the form of the Harpoon Block II missiles equipping Collins class, Adelaide class and Anzac class platforms.

Harpoon uses GPS-aided inertial navigation to accurately deliver its 224 kg high-explosive blast warhead.

Ironically, while Harpoon is primarily an anti-ship weapon which now has some land attack ability, Raytheon has said it will enhance Tomahawk Block IV, a land attack missile, to also enable it to attack ships.

This will be done by integrating a seeker that will detect ship electronic signatures; making the existing datalink faster and giving it more bandwidth; and by upgrading Tomahawk's warhead, allowing it to penetrate the armour of 21st century warships.

Raytheon Australia declined to discuss any details of the Tomahawk, with a spokesman describing cruise missiles as "a sensitive subject".

However, Block IV unit cost is believed to be about US$1.4 million, with command and control systems, notably the TTWCS, adding about another 30 per cent to the cost of any initial bulk missile order.

As an example, the 24 Tomahawk Block IV missiles and weapon control systems, plus associated equipment and services, being purchased by Spain are expected to cost about US$150 million.

The missile's modular design enables easy integration of potential future payloads including the Joint Multi-Effects Warhead System, which is intended to provide increased flexibility and lethality in denied environments against hardened targets.

The Block IV also features a 15-year recertification interval, an attribute that will see the missile's service life extend well beyond the introduction of its successor, currently planned for 2016.

Four companies - Boeing, MBDA, L-3 Titan and Raytheon - are currently evaluating material approaches, refining the concept of operations and systems architecture and conducting risk assessment for an Affordable Weapon System (AWS) which is intended to fulfil requirements for a sea-based, stand-off strike mission system with a unit cost of US$250,000.

The US Naval Air Systems Command has specified that AWS must have a shorter engagement time between weapon launch and target kill than Tomahawk, but how this goal is achieved has yet to be decided.