HANS J OHFF. Horse for Courses: Nuclear and Diesel-Electric Submarines

Aug 2, 2017

Arguing for a review into nuclear-powered submarines former PM Abbott laments that ‘the RAN will take delivery of a class that will have less power, less range, less speed and less capability … and that it will come into service about a decade later than would be optimal at a time when strategic circumstances are changing against us.’

Defence Minister Marise Payne reminded Mr Abbott that ‘Australia lacks the qualified personnel, experience, infrastructure, training facilities and regulatory systems required to design, construct, operate and maintain a fleet of nuclear-powered submarines. [And] developing a sovereign nuclear-submarine fleet would come at a very substantial cost premium to our conventional fleet’.  But more should be said.

Nuclear-powered attack submarines (SSNs) are about force projection. They exercise sea control in support of surface strike groups, shadow ballistic missile submarines, deny enemy battle groups access to zones of interest. Thus, setting Australia’s lack of industrial and operational capabilities aside, the debate needs to be had whether an Australian government should seriously consider deploying properly armed SSNs. That is for a Middle Power like Australia to enter the nuclear arms race.

Securing the sea lanes of communication and seaboard remains paramount in Australia’s national defence strategy.  Diesel-electric submarines (SSK) excel in the littoral or coastline waters, extending to the Continent’s northern and north-western approaches. Further, Australia’s strategic interests are well served by providing the US Navy with the layer of submarine operational capability it needs but does not have. In the Australian – USA defence alliance RAN submarines are valued for their littoral capabilities that form a natural extension to regional US nuclear submarine operations.

The United States Navy (USN) and the Royal Navy (RN) submarines are powered by highly enriched (HEU ≤ 90% U-235) weapons-grade nuclear material that does not ordinarily require replacing during an operational 30-year submarine life-cycle. The French Navy is running its submarines on high density, monolithic,  low-enriched uranium (LEU ≤ 10% U-235) that require periodical refuelling.  Whilst a typical peace-time deployment would be similar for nuclear and diesel-electric submarines (50 to 100 days), the autonomy of a nuclear-powered submarine would ordinarily only need to be suspended for taking provisions and weapons, or repairs and maintenance, and for crew change.

In addition to long endurance, nuclear power provides an SSN with a sustained speed of >30kt. This submerged speed translates into far-reaching, covert mobility that outperforms surface units in any navy’s inventory. It is a valuable capability that a SSK lacks. But the size of a SSN limits effective deployments in the littorals and estuaries. Consequently, high speed in coastal regions cannot be exploited as in the open ocean and, together with a big submarine’s echo strength, increases the probability of counter-detection.

Thus, there are operational missions for which SSNs are not suited. The size of the USN VIRGINIA-class (length 115m, beam 10.4m, ~7,800 tonnes submerged displacement) and the RN ASTUTE-class (97m long, 10,4m beam, ~7,000t), arguably make them too long and too high from keel to periscope to operate effectively in shallow waters. Neither is the French BARRACUDA-class (99.4m long, 8.8m beam, ~5,300t). Whilst smaller the class is still not particularly suited to operate in the littoral zones compared to smaller, low-signature, SSKs

Conversely, due to a lack of mobility, the SSK is not suited for support of fast moving surface forces. A sustainable speed of less than one third of an SSN renders a SSK vulnerable to detection during snorting to recharge the batteries. The displacement of the submarine determines the required power, number and size of the diesel generators, the batteries, and the snort and exhaust masts.

Chief of the German Navy, Vice Admiral Krause, was correct when he explained that non-nuclear submarines are ‘vehicles of position.’ The former submarine commander explicates that despite advances in sonar technology, detecting and targeting submarines in confined and shallow waters, where variable salinity and thermal zones are present, remains extremely difficult. In these littoral waters non-nuclear-powered submarines are given the operational task of intelligence gathering, surveillance and reconnaissance (ISR). They are charged with the protection of shipping lanes, choke points and harbours. Non-nuclear-powered submarines, the Admiral emphasises, are also suitable to precursor operations, i.e. ‘prepare a battle space prior to major operations.’ Their first task is ‘to survey the area, identify threats and explore and assess the environment.’ Whilst perfectly suited to an ISR role in littoral waters, once hostile operations commence, the modern non-nuclear-powered submarine can readily become a lethal weapon platform either as a hunter-killer or in support of a battle group.

VAD Krause’s view is supported by DCNS – now NAVAL Group – Director of Submarine Design Division, Vincent Geiger and former submarine commander, Benoît le Masson. After decades of force projections on the high seas the French experts claim that smaller and middle powers are now emphasising the protection of their maritime borders.

To operate a submarine at less than 2 knots only meters above an irregular seabed, or to bottom for a prolonged period undetected, can best be achieved by a SSK. Notwithstanding the advances made in anechoic tiling and the benefits of ambient noise prevalent in shallow waters, the acoustic signature of the nuclear reactor and its associated appurtenances will rarely be hidden. The infrared signature of a nuclear power plant is detectable in nearly all sea states in the thermal structure of wave patterns. Close to the ocean floor the cooling-water intake on SSNs could be prone to collecting contaminants. In contrast today’s conventional submarines are extremely quiet, with very low infrared and magnetic signatures. Powered by Li-ion batteries and AIP propulsion these submarines can operate at patrol-quiet-state or sit on the seabed for several weeks without surfacing.

Australia’s liquefied gas, iron ore and coal – the country’s major earners – are exported from designated ports and terminals on the north-west and east coast of Australia. The current off-shore oil and gas fields are in waters of less than 200m depth. Safeguarding these installations are paramount to the country’s economic security.

The Australia governments’ – past and present – strategic interests call for greater submarine range and longer patrol endurance. This would have influenced the government to select a submarine similar in displacement to that of a SSN. But increased size compromises stealth. Thus, if sustained long-range operations are required Australia’s defence interests would be better served by forward basing submarines. Clearly, the government’s choice of the SHORTFIN BARRACUDA Block 1A concept unites design and building risks, high program costs and an extended delivery schedule. It is a decision that promises little or no capability gains.

Hans J Ohff is Visiting Research Fellow The University of Adelaide and former Managing Director and CEO of the Australian Submarine Corporation  

The attached article appeared in Engineers Australia on 15 July 2017


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