New torpedoes in the water

US-Australian cooperation has resulted in a new and significantly improved variant of the veteran Mk 48 heavyweight torpedo.
The Royal Australian Navy will shortly receive its first deliveries of an interim replacement heavyweight torpedo, with Initial Operational Release (IOR) of the highly-sophisticated Mk 48 Mod 7 ADCAP CBASS (Common Broadband Advanced Sonar System) torpedo scheduled for late 2007.

CBASS will replace the Mk 48 Mod 4 heavyweight torpedo currently in service aboard the RAN's Collins class submarines.

The interim delivery (thought to be 20) of Mk 48 Mod 6 ACOT (Advanced Common Torpedo) weapons will meet certification requirements for HMAS Waller, currently being upgraded for the torpedoes as part of her Full Cycle Docking, pending ramp up to the CBASS production run.

The delivery of Mod 6 ACOT torpedoes in late 2006 and Mod 7 CBASS torpedoes in the second quarter of 2007 will enable simultaneous IOR for both the ACOT and CBASS weapons.

All remaining torpedoes will be delivered as Mk 48 Mod 7 CBASS and the interim Mk 48 Mod 6 ACOTs will be upgraded to Mod 7 by the DMO's Guided Weapons Sustainment-West facility when the required hardware is available. This is relatively simple due to the open-architecture design of the control-and-guidance section.

CBASS is the outcome of a little-known but highly successful US-Australian Armaments Cooperative Project to jointly develop, produce and support the Mod 7 torpedo, the Memorandum of Understanding for which was signed between Defence and the US Navy in March 2003.

The project scope includes the acquisition of the weapons, associated logistic support, weapon system interface equipment, operational support, test equipment and transition into service.

Project Sea 1429 Phase 2 involving expenditure of A$430 million was approved on 25 March 2003 - just six days prior to signature of the torpedo development MOU with the US Navy. This figure includes CBASS development and purchase, and the upgrade of the initial delivery of Mod 6 torpedoes to Mod 7 CBASS standard.

This sum also covers the cost of modifications to the six Collins class submarines necessitated by the 118 kg weight difference between the Mod 4 and the Mod 6/ Mod 7 torpedoes. These involve strengthening the weapon handling system and weapon embarkation system, upgrading the weapon discharge system, and weight and stability changes for trim and handling.

Defence says that to date, no major issues have been encountered, with the modification implemented and verified on the Weapon Handling and Discharge Training rig at HMAS Stirling.

The modifications to HMAS Waller are nearing completion, and the five other submarines will be progressively upgraded to handle the CBASS torpedo as part of their docking programme through to 2010.

The delivery of CBASS weapons into inventory is matched to the Replacement Combat System installation project (Sea 1439 Phase 4A) and the physical modifications to the submarines.

Development of CBASS has been handled by a joint Australian-US project office at the Washington Navy Yard, with a detachment at the Naval Undersea Warfare Centre at Newport, Rhode Island. Raytheon US has also been involved as the original equipment manufacturer.

In-water testing began in September 2004, and included developmental tasting in Western Australia in September and December 2005, the latter at which HMAS Rankin acted as the target for a CBASS prototype fired from a US submarine.

Operational testing was completed successfully in March this year by the US Navy's independent testing and evaluation organisation and on 22 June, the USN's Program Executive Officer for Submarines, Rear Admiral Willy Hilarides, authorised the Undersea Weapons Program Office to procure the full order of torpedo hardware for both the USN and the RAN.

The USN is expect to purchase more than 1,000 upgrade kits for its current inventory of Mod 6 torpedoes, with Initial Operational Capability scheduled for September this year and Full Operational Capability expected in 2011.

The 533mm Mod 4 submarine-launched torpedo now used by the RAN is an analogue weapon weighing 15,445 kg which includes a 292 kg high explosive warhead. Operating with or without wire guidance, in the latter case utilising its own active/passive sensors for a fire-and-forget capability, the Mod 4 was designed to attack fast, deep-diving nuclear submarines and high-performance surface ships.

The Mod 5 ADCAP enhancement included all-digital guidance and control systems, digital fusing systems, and propulsion improvements which added speed, depth, and range capability.

Mod 6 involved the introduction of an open architecture guidance-and-control section based on COTS signal and data-processing hardware and an industry-standard Ethernet databus.

Mod 7 CBASS will, in conjunction with advanced broadband sonar signal processing algorithms, deliver enhanced detection and prosecution of diesel-electric submarines operating in shallow water and employing advanced countermeasures, while retaining its deep water capabilities. Although the Mod 7 utilises the same Mod 5/6 body (and warhead), this is brought back to new-build status and includes a new guidance and control section.

The Maritime Operations Division (MOD) of DSTO has contributed signal and data processing algorithms for the torpedo via the Advanced Processor Build spiral development process employed for periodically enhancing the torpedo's performance.

To undertake this research and development, the MOD obtained a variety of software and hardware tools from the US Naval Undersea Warfare Centre for the DSTO Torpedo Systems Centre in Edinburgh, South Australia. These tools have enabled the emulation of the torpedo's detection and tracking performance and the simulation of the torpedo's entire operation.

The main tool, called the Torpedo Analysis Facility, enables Australian stakeholders to study in high fidelity the performance of the weapon in the laboratory environment, in scenarios and environments which are unique to Australia.

Shortly the system will be used to undertake a joint study with the US to determine the performance of the weapon in scenarios and environments of interest to both countries.

Although the overarching cooperation agreement expires in 2013, Defence says both parties are committed to improving the through-life capability of the weapon, and are already discussing the next iteration of the MOU.

While Defence declined to comment on areas of future interest, these are thought likely to include covert sonar and other stealth developments such as reduced radiated noise.

By Julian Kerr, Sydney