ast month the generic roles and functions of a submarine were mapped into the Australian context and some analysis was carried out to identify any aspects of the Australian requirement that stood out as unique. One requirement that warranted further discussion was that of submarine “endurance” and “range”. It was acknowledged, and is largely undisputed in military circles, that the Area of Operations (AO) for Australia’s future submarines will be both large and distant. Are the Australian range and endurance requirement unique, or perhaps just unusual? Can the Australian requirement be met by a Military Off The Shelf (MOTS) submarine, and if not, by how much does a MOTS submarine miss the mark? Finally, if the MOTS submarine does miss the mark, how can the requirement gap be met economically by alternative solutions? There is little point in procuring a future submarine that cannot meet ADF peace and wartime endurance and range needs. However, noting the high cost that would be borne by the taxpayer for the procurement of a unique submarine design and the national consequences if any of the significant own design project risks are realised, all options with respect to meeting endurance and range requirements must be considered.
12th May 2011
Last month the generic roles and functions of a submarine were mapped into the Australian context and some analysis was carried out to identify any aspects of the Australian requirement that stood out as unique.
One requirement that warranted further discussion was that of submarine “endurance” and “range”. It was acknowledged, and is largely undisputed in military circles, that the Area of Operations (AO) for Australia’s future submarines will be both large and distant.
Are the Australian range and endurance requirement unique, or perhaps just unusual? Can the Australian requirement be met by a Military Off The Shelf (MOTS) submarine, and if not, by how much does a MOTS submarine miss the mark? Finally, if the MOTS submarine does miss the mark, how can the requirement gap be met economically by alternative solutions?
There is little point in procuring a future submarine that cannot meet ADF peace and wartime endurance and range needs. However, noting the high cost that would be borne by the taxpayer for the procurement of a unique submarine design and the national consequences if any of the significant own design project risks are realised, all options with respect to meeting endurance and range requirements must be considered.
A submarine’s endurance is defined as “the number of days the boat can remain at sea unsupported” Factors effecting this are:.
Fuel load is a primary contributor to the period of time a submarine can spend at sea. If one discounts leaving harbour with a full battery and returning with it fully discharged, the total energy requirement of a submarine, the combined mission hotel and propulsion load, has to be met by the carriage of fuel, including that used for Air Independent Propulsion (AIP).
Clearly the propulsion load has an effect on the usage rate for fuel.
Hull and Equipment Efficiencies
Efficiencies in a submarine’s hull design and equipment affect submarine endurance.
A decrease in hull size for a given capability represents an efficiency that will improve endurance. Flowing from that, technological advances that reduce equipment sizes and weights without reducing capability are generally welcomed by submarine designers. They allow for smaller hull sizes and simplify equipment layout.
Hull shapes optimised to reduce hull form drag and the use of specialized hull materials or paints which help reduce skin friction and can also affect operational endurance.
The selection of highly efficient equipment such as permanent magnetic motors, highly efficient diesel engines and generators, efficient static inverters for power conversion and low voltage technology in platform and mission system electronic systems all serve to reduce energy consumption throughout a patrol. Modern technology also allows for the removal of a number of energy and space consuming components. For example, lithium ion batteries eliminate the need for battery ventilation, cooling and hydrogen elimination systems. Automation and the shift to totally integrated platform monitoring and control systems helps reduce the number of watch keepers required, thereby minimising crew numbers which in turn assists in reducing submarine size requirements and reducing hotel loads.
Reliability, Maintainability and Redundancy
Reliability is a function of equipment selection and design, age and usage rates, maintenance philosophies and maintenance scheduling. Failure of critical systems due to normal wear and tear or battle damage and subsequent non repair can terminate a patrol as will the accumulation of failures and non-repair of less critical systems. Unlike fuel, reliability cannot be reset by pulling up alongside a support base or tender. Compounding the problem, the reliability clock starts ticking as soon as equipment is switched on after the last major overhaul.
The ability to effect onboard repairs in the event of equipment failure is also an important consideration; an ability influenced by the capabilities of monitoring systems and diagnostic tools, the level of technical and maintenance documentation available, the competency of maintenance staff and the availability of the correct spares.
Available stowage space for spares, consumables and food can affect submarine endurance.
Refrigerated stowage space can be a particularly limiting factor. Whilst space can be found for additional patrol supplies, if required, this is not true for perishable items.
The storage capacity for potable water can also constrain endurance if fresh water generation is not a possibility.
Crew endurance is an input to overall submarine endurance with the provision of space, amenities and facilities helpful in maintaining crew moral. Improving space for crews can be achieved by automation, which in turn can reduce crew size requirements and associated food and other stowage space requirements.
Payload capacities, which are traditionally limited on submarines, can have an effect on “mission endurance”. Once a submarine has used all of its effectors, be they torpedoes, missiles, mines or the deployment of Special Forces, the mission will end. Specific tasking, such as land strike or mine laying, where a large percentage of the total payload is consumed in a single event, can shorten mission endurance. The situation is worsened by the fact that there is now a greater variety of effectors that can be embarked. During high intensity conflicts where a variety of effector types are loaded for mission flexibility reasons, it may be possible to consume all embarked torpedoes after encounters with only a few enemy task groups.
Before moving off the topic of endurance, it is worth explicitly pointing out that hull size does not contribute greatly to a submarine’s endurance.
Whilst a larger submarine can carry greater fuel loads, they require more fuel to push themselves through the water and have bigger diesels, bigger batteries, bigger main motors, more auxiliary equipment and larger crews.
There is little question that larger hull sizes improve crew habitability enabling better crew accommodation, perhaps with dedicated cabin arrangements, across a couple of decks, as opposed to a smaller submarine where crew areas are squeezed into spaces left over after operational related space allocations have been made.
Finally, whilst a larger hull size does increase the payload capacity, it is not enough to influence total mission endurance significantly. A 3,350 tonne Collins class submarine carries 22 weapons, a 2455 tonne Upholder Class submarine carries 18 weapons, a 2430 tonne S-80 carries 18 weapons, a 1900 tonne Dolphin class submarine carries 16 weapons, an 1830 tonnes Type 212 submarine carries 12 weapons and an 1810 tonne Type 209 submarine carries 14 weapons. Increasing the number of weapons from the Type 214 to a Collins Class submarine may only increase the total mission endurance by hours or days.
It is accepted that larger submarines tend to have greater endurance, but the increase is not linear. Manufacturers’ design data and Navy empirical data support this claim. In the mid-eighties, over a period of 29 days, the Argentinean Type TR-1700 submarine ARA SANTA CRUZ travelled 6,900 nautical miles from the Bay of Biscay to Mar del Plata. A distance of 600 miles was transited on the surface; the remainder either submerged or snorkelling. This is the longest publically recorded submerged/snorkelled run by a conventional submarine. The boat averaged 10 knots. She arrived with a 50 per cent reserve of fuel and her captain, Commander Carlos Rela, indicating that she could have returned to Emden, Germany without refuelling. “Even the food would have been sufficient”. Australia’s 2400 tonne Oberon Class submarines had similarly impressive range and endurance capabilities. German Type 214 and French Scorpenes have advertised endurances of more than 50 days and Pakistan’s Agosta 90B AIP submarines have deployed for more than 60 days.
Our much larger Collins Class submarines have only achieved a maximum deployment of 55 days.
Range and Radius of Action
Range is defined as “the absolute distance a submarine can travel unsupported”.
Range is important in the Australian context as the distance between our major submarine support bases and likely operating areas is large. This is true even in Defence of Australia tasks. This means that transit distances will always be large.
Large transit distances have an impact on a submarine’s endurance. Transits are generally conducted at as high a speed as is technically and operationally possible. The amount of energy required to push a given submarine through the water varies with the cube of the speed, i.e. doubling a submarine’s speed increases energy consumption by a factor of eight. Thus, high speed transits erode endurance.
A Range of Options
All conventional submarines are restricted in the speed at which they can transit. A maximum physical speed of advance (SOA) of between 10 and 12 knots is all that is possible. At high SOAs there is a need to snort regularly. The maximum speed at which any submarine can snort is about 10 knots. Loss of hydrodynamic control, causing depth excursions that results in the snort mast submerging or, worse, the submarine broaching, is one reason. Other reasons include excessive vibration in periscopes or optronics masts and/or mast damage associated with high speed through the water. Last, but not least, the generation of large detectable water plumes and wake trails inhibit snort speeds in areas where ASW forces oppose a submarine, particularly in areas where there are flat seas.
Transit time is wasted operational time. Long transit distances delay a submarine’s arrival into an AO and eats away at the achievable radius of action. Recent analysis by ASPI’s Andrew Davies reveals that, with respect to a South China Sea patrol, a 50-day trip originating from and returning to HMAS STIRLING would only yield half the time on patrol in the AO when compared to the same duration trip originating from and returning to Guam. Putting a slightly perspective on the same theme, long transit distances also render a submarine operationally mute for long periods of time if it has to transit all the way home to repair a defect or effect a weapon reload.
Long transit distances demand alternative solutions; shortened logistic support lines are a high priority for all operational commanders, particularly Australian operational commanders.
Forward Basing and Tenders
One solution is to forward base our submarines. Australia’s diplomats and Defence staff should and almost certainly do, work in peace time to ensure we have access to bases of other like-thinking nations in the lead up to and in time of conflict.
Consistent with and complimentary to this theme is the use of submarine tenders - that is vessels with specialist submarine support capabilities that can be deployed forward to assist in forward and/or long term deployments. They have specialist workshops such as machinery, electrical, battery, electronics, periscope, and weapon, along with medical facilities and other services such as shore supplies, refuelling and communications. They have the added benefit that they can be called upon to provide support for disaster relief in peacetime. They can also serve as submarine trials support ships. Nations with needs with respect to submarine “reach” have opted for forward basing and tenders; as part of the USN’s expeditionary maintenance model, USS FRANK CABLE operates out of Guam and USS EMORY S. LAND will soon be operating out of Diego Garcia.
Those that argue against the reliance on forward bases and tenders do so on the grounds that such an approach would signal an operational commander’s intentions with respect to the employment of submarines and that forward bases and tenders are vulnerable to attack.
The mere fact that a submarine is active, or is even suspected of being active, in a particular region can deny the enemy the use of that area. This was almost certainly foremost in the minds of the British Government when it announced the presence of submarines in the South Atlantic through the media, although the sinking of the ARA BELGRANO was a great follow-up move. Consider the hypothetical scenario where Australia commits to the deployment of our future submarines to the South China Sea. When an enemy operative sends a coded SMS to signal that one of our boats has departed HMAS STIRLING, it is true that five days later the enemy will not know exactly where the submarine is, but they will know that it is south of the equator and heading north. When the same thing happens to a submarine operating out of Guam, the enemy will not know exactly where the submarine is, but they will understand that it could be anywhere in the AO. The deployment of a submarine tender can also send positive sea denial signals, without revealing a submarine’s datum. Conversely, those skilled in the art of deception might also use a tender to advertise the presence of submarines in an area where they are in fact not deployed.
It is accepted that forward bases may be vulnerable to enemy attack. Whilst operations from forward bases are undoubtedly feasible in peacetime and in the lead up to war, it may not be possible as or after hostilities commence. Forward base unavailability risks can be mitigated by having a range of alternatives available, and submarine tenders can assist greatly in this regard. Having submarine tenders also mitigates the risks associated with attacks on Australian support facilities such as HMAS STIRLING and ASC.
Having capable submarines active in the AO is the ultimate objective of operational commanders. Low submarine numbers, particularly when coupled with long transit distances, eats away at this objective.
The Defence White Paper (DWP) calls for Australia to acquire 12 new submarines. Estimates of the budget required for Australia to acquire 12 uniquely designed submarines run at more than $36B compared with $10B to acquire highly capable MOTS submarines.
For a number of years Australian Governments, both Liberal and Labor, have sought fiscal responsibility through budget surpluses. Prime Minister Gillard is continuing down the fiscally conservative path. There is no appetite in Government for expensive and risky Defence projects. Few commentators would argue that pressure associated with a new design or evolved Collins replacement for the Collins Class submarines will see the numbers drop from 12 to probably eight, possibly six. Even if forward basing and tender options are exercised, this equates to a less effective submarine force because of a reduced number of possible days in the AO.
The low cost and risk of acquiring 12 highly capable MOTS submarines would be a responsible and highly regarded decision by Defence that would almost certainly win it wider support, including amongst Treasury and other financial guardians. Having a larger number of smaller and less expensive submarines carrying 14 to 18 weapons each provides the ability, for any given budget, to put more weapons into the field and simultaneously in more locations.
Finally, it is worth pointing out that having 30-month full cycle dockings, as Australia is trying to achieve with its Collins Class submarines, has the same effect on the number of achievable days in the AO as having fewer submarines does. Long docking cycles must be avoided for our future submarines.
Of all the peacetime roles discussed last month, ISR is the one that requires the greatest radius of action. In fact, it may be that the ISR role, on account of lack of weapon depletion throughout and the benefits associated with time spent in the area of intelligence collection and surveillance, is likely to be the defining radius of action role.
Australia has never conducted deployments into the northern hemisphere without visiting a forward base of some sort during its mission. It is hard to imagine that the Australian requirement cannot be met with a MOTS submarine. Recent claims that MOTS submarines will fail to achieve the endurance based on crew space constraints are false. This author has been to sea on Oberon submarines, whose empirical endurance figures exceed those of Collins, and modern MOTS submarines such as Type 214s: the accommodation standards on the modern MOTS submarines exceed those of the Oberon Class.
In the ‘Deterring and Defeating Attacks on Australia’ role discussed last month it was determined that Australia’s future submarines would play a significant role in interdiction operations around Indonesian, Timorese and Papua New Guinean straits and territorial seas, particularly those areas where the ADF did not have complete air or sea control. They might also act as ASW guards around crucial straits. They could also deploy into the forward AOs close to enemy naval ports and enemy logistic hubs to conduct reconnaissance, maritime strikes and ASW, land strike, offensive mine laying and Special Forces insertion. Figure 1, which shows the radius of action of a Spanish S-80 doing a 10 knot SOA transit to Lombok and slowing to an ambitious 6 knot SOA in opposed areas, demonstrates this is achievable with a MOTS submarine.
The ‘Contributing to Stability and Security in the South Pacific and East Timor’ strategic interest in the DWP is also satisfied through the radius of action capabilities illustrated in Figure 1.
It has been suggested by some that Australia has unique range and endurance requirements and that a unique submarine design is required to fulfil this requirement. Whilst potentially unusual, the range and endurance requirements for our submarines are not in fact unique. During World War II, US Navy, Dutch and Royal Navy submarines home ported as far south as Albany, WA and patrolled widely across the Pacific and Indian Oceans. German and Japanese submarine also covered vast patrol areas. During the Cold War, Russian conventional submarines operated deep into the Pacific and Indian Oceans. Other nations’ modern conventional submarines are known to transit long distances. A multi-national anti-piracy task force operating off the East Coast of Africa includes European submarines and it is noted that Peruvian submarines regularly exercise off the U.S North Atlantic coast.