Undersea Technology: A tale of two lightweight torpedoes | ADM August 2012

The ADF’s torpedo inventory is growing, with two new lightweight torpedoes, together with Mk-46s and various Mk-48 heavyweights, ADCAP and otherwise, all in their various warshot, ASROC, dummy, training and high altitude guises. Enough, one suspects, to make even a Costco shelf-stacker blink.

Of course, the two new lightweight torpedoes (LWT) we are talking about are the Eurotorp MU90 and its main international competitor, the Raytheon/USN Mk-54 hybrid.

But this not a pretty tale. The MU90 Impact was selected over the Mk-54, the Bofors TWS 90 and the GEC-Marconi Stingray, as the preferred choice for the ADF’s primary ASW airborne weapon system.

But management failings, including that of the initial selection, and other factors have seen the role of the MU90 LWT reduced to that of ship-launched LWT aboard the Anzac (FF H) and Adelaide (FF G) ships, while the Mk-54 is now being acquired in considerable numbers to recover the all-important airborne ASW weapon capabilities that lightweight torpedoes are best at!

So how has this switch from one highly regarded weapon system to that of its main competitor come about, and why do we need them both? Perhaps we should look at their respective capabilities.

MU90 Impact LWT

The MU90 is a fire-and-forget weapon designed to counter any type of nuclear or conventional submarine, whether acoustically coated, deep and fast-evasive, deploying active or passive anti-torpedo measures.

The MU90 torpedo can be deployed from any type of surface and air platform including missiles. It can also be encapsulated into continental shelf mines as well as launched by submarines. Its unmatched deployment altitudes and extremely long stand-off launching capabilities allow the ASW forces to cope with the threat posed by the modern submarine-launched antiair- missiles (SLAAM).

Of extremely long endurance, the engagement distance is beyond 12,000 metres, whatever the submarine depth. The MU90 operates without any speed degradation and without any limitation of salinity and temperature at depths >1,000 metres or as shallow as 25 metres whilst retaining navigation capability up to three metres. It is currently in mass production and it is entered into service with the French, Italian, German, Danish and Polish Navies. It has been accepted by the RAN for introduction into service following full operational test and evaluation and final ship modification.

Mk-54 LWT

Derived from the need for a smaller, lighter, but cost effective advanced torpedo that could be deployed as an airborne weapon system and from smaller naval vessels, the Mk-54 lightweight torpedo was developed under a broad ranging ‘Team Torpedo’ partnership between the US Navy and Raytheon.

According to the manufacturer, Raytheon, the Mk-54 meets today’s need for a lightweight torpedo capable of dealing with submarine threats in both deep and shallow water — and in various acoustic environments. The Mk-54 can be deployed from a surface ship, helicopter or fixed wing aircraft to track, classify and attack underwater targets. It uses sophisticated processing algorithms to analyse the information, edit out false targets or countermeasures, and then pursue identified threats.

The Mk-54 program leverages torpedo technologies from the Mk-50 and Mk- 48 ADCAP (advanced capability) programs. It also employs the Mk-46 warhead and propulsion subsystems, resulting in a low cost weapon that the company claims meets all performance requirements for littoral warfare.

So where are we today?

Back in November 1999 Thales was selected to undertake the Phase 1 project definition studies based on the Eurotorp MU90 LWT with the presumption that this would lead to the acquisition of that torpedo type (and thereby the elimination of any competition for Phase 2).

The Source Evaluation Report (SER) indicated that the MU90 was regarded as being the most developed weapon of the four torpedoes considered. While this was undoubtedly the case, the SER also saw the MU90 as an ‘off-the-shelf’ acquisition, an extraordinary error since this was not the case. To cap it all, the Defence Minister was then advised that the MU90 had been selected and that it was the only ‘inservice’ weapon offered!

Indeed it wasn’t until early 2004 that the DMO recognised that the torpedo was not in-service with any other nation and that far from being the risk free acquisition earlier assumed, there had been technical and production problems with the torpedo.

But the Phase 2 torpedo acquisition and integration phase was already underway without a full understanding of the risks, especially those involved in the integration of the MU90 onto various platforms, including air platforms (where surely the real merits of a lightweight torpedo lay). Thus, some 13 years since Phase 2 was approved and funded, the MU90 has yet to be accepted into ADF service despite a cost to date of nearly $250 million.

When the MU90 was selected the intention was to equip the AP-3C Orion and the RAN Seahawk and SeaSprite helicopters with the LWT system. But the SeaSprite was cancelled in 2008 and integration on the Orion and Seahawk was removed from the scope of JP2070 in early 2009 ostensibly because of the risk and difficulties involved.

These included a significant underestimation of the full cost to integrate the weapon onto the various platforms and delays and difficulties being encountered by other projects that were upgrading the platforms with which the torpedo was to be integrated.

Plus the decision to purchase 24 MH-60R Seahawk Romeo naval helicopters for the RAN and to equip them with FMS-acquired Mk54 lightweight torpedoes, rather than the NH-90 helicopter, equipped to fire the MU90, was another nail in the coffin for an airborne MU90 capability. And what may be seen as a clincher in respect to the Mk-54 as the ADF’s airborne weapon of choice, lies in the US Navy’s successful launching of the first Mk-54 lightweight torpedo from a P-8A Poseidon aircraft during a test event late last year.

It is thus quite certain that the P-8A Poseidon aircraft, to be acquired later as replacements for some of the AP-3C Orion MPA fleet, will be equipped to drop the Mk-54 torpedo.

Thus the ADF’s inventory of new lightweight torpedoes will comprise the Eurotorp MU90 as a shipborne weapon, possibly including an anti-torpedo role, and the Raytheon/USN Mk-54 as the only air launched ASW weapon. For Thales and Eurotorp JP2070 has not been a happy experience - quelle dommage!