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Ed. Note: During the Royal Navy submarine centennial Captain Rask held a briefing in Lancaster, England about submarine operations in The Baltic Sea.He was later asked by Taiwan Defense Affairs to write an article about submarine operations in Taiwanese waters. It was printed there in Volume 1, No. 3, Spring 2001. It is reprinted here with permission of Taiwan Defense Affairs.

Captain Rask states he has never been to Taiwan but the shallow area of the Taiwan straits is, in many ways, similar to the situation in The Baltic.

The Strategic Framework

A quick look at the map or at a chart covering the western part of the Pacific immediately shows the observer the strategic position of Taiwan.

Taiwan is located almost on the Tropic of Cancer, separated from the Chinese mainland by the very narrow and shallow Straits of Taiwan. The straits are just some 80-100 nautical miles wide. The important sea line of communications between Europe-Singapore and Japan runs through the straits. The straits and undisturbed shipping along that sea route therefore have a high strategic value for many countries. The straits have in that respect a worldwide interest. A conflict in the straits, due to the high interests at stake, will immediately draw attention from several strong maritime nations in the area and elsewhere.

The straits also have an important operational and tactical value for the People’s Republic of China (PRC). Chinese military and civilian coastal shipping along the eastern coast of China has to run through the straits to connect the southern and northern parts of China. Taiwan is located almost on the middle of the eastern seaboard of China. From Taiwan, it is possible, at least temporarily, to threaten the shipping along the coast of China, and thereby cut the PRC sea lines of communication. Taiwan could easily be a military platform (similar to a carrier) from which a serious air and naval threat to the PRC can be established.

Finally, the free access to the high seas and a free navigation along the sea routes to and from Taiwan are essential to the national survival of Taiwan due to Taiwan’s needs as an export-oriented economy.

The Straits of Taiwan therefore, in many respects, represents a classical Maritime hot spot on the globe. That hot spot can easily be the spark in the powder-barrel that threatens the stability in the region. Naval presence in such an area is paramount for nations that rely on shipping along the sea lines both for their survival and for the increase in their economy. A strong naval presence from many countries with different interests at the same spot of ocean can be a stabilizing factor, but can also rapidly increase the tensions in the area.

On paper, the PRC maintains a strong navy with a strong submarine force. A look at the order of battle tells us that many of the ships are of older origin and not especially suitable for operations in shallow water. The strength of the PRC Navy lies mainly in the large number of missile attack boats and its substantial amphibious capability. That naval force can easily disturb the free navigation to and from Taiwan with a naval blockade if PRC decides to do so. The possibility of an invasion lies also at hand. The PRC submarine force consisting of a range of different boats; SSBN, SSB, SSN, SSG, SSK and SS all have their different roles to play, not necessarily against Taiwan in case of a conflict. Several boats are of an older design with a low battle potential. The SSBN and SSN needs normally deeper water than the straits can provide.

Submarine operations with small submarines in such an important area can be very successful. From the U.S. submarine attrition war against Japan during WWII, there are numerous examples of successful submarine attacks against the Japanese shipping in the Straits of Taiwan (Formosa) and along the eastern coast of China. Legendary is the eleventh war patrol of USS BARB (Commander Fluckey) in December 1944-February 1945, the third war patrol of USS TANG (Commander O’Kane) June-July 1944 and the fifth war patrol of USS TANG (Commander O’Kane) September-October 1944. On that last patrol the submarine operated in the southern reaches of the East China Sea; specially the reach between Northwest Formosa and the China Coast. That area was dangerous due to minefields to the eastward and a hostile coast to the west. The famous USS TANG was lost on that patrol, due to a circular run on one of her own torpedoes.

The U.S. submarine war of attrition successfully choked off the supply of food, crude oil, rubber and other vital industrial raw materials, thereby strongly contributing to Japans ultimate unconditional surrender.

The main defence strategy for Taiwan obviously has to be to avoid being choked by a PRC threat of war of attrition or that such a war breaks loose. An important part of the strategy must therefore be to build strong relations to important naval powers that can come to assistance in case of an increased tension in the area. The only country with a true naval capacity and base facilities in the vicinity (Okinawa) for such a conflict, is the USA. Another important part of the strategy must be to build up an air and naval force capability that can take the first blow in case of a conflict. Such a strong force could easily increase the defence planning difficulties for PRC.

A strong submarine force can be the cornerstone in such a force structure. Modem submarines can take the war to the enemy along the whole China coast, which is a very valuable asset. They are unpredictable in their operations and extremely difficult to detect and destroy. Modern submarines can therefore change the whole strategic situation in the East China region in favour for Taiwan and it’s security Policy. Modem submarines must therefore stand at the top of the Taiwan shopping list.

Operational Conditions-Implications on SM Warfare

When looking at the coast and the surrounding waters of Taiwan from a submariner’s point of view, it is important to recognition the following features:

Taiwan has, since 1949, been the focal point between two strong military opponents; USA and China. In this respect, the strategic situation of Taiwan is very similar to the one that Sweden faced during the Cold War. Sweden was in between NATO and the Warsaw pact, with the Soviet Union just some hours-sailing time away. Taiwan’s immediate proximity to China makes it difficult even for U.S. forces to constantly control the waters surrounding Taiwan. Therefore Taiwan has to have military forces that are strong, so they could take the first blow if PRC decides to attack Taiwan. Now and then, China has increased its naval presence and thereby the tension in the area, by conducting exercises in order to show naval strength and to threaten Taiwan. At some stages this has caused the U.S. to increase its naval presence in the area, and as a result, the tension slowly decreases. But the message from PRC is crystal clear: we have the capabilities to threaten and disturb your import and export shipping! The threat and the PRC exercises can, if not calmed down by U.S. naval presence, easily take the world to the brink of the Third World War. The Taiwan strategy must therefore be clear, foresighted and from the PRC side, predictable. A firm appearance from Taiwan in every military aspect concerning the PRC is absolutely necessary. Otherwise the PRC may think that Taiwan is soft and will not use its military forces and/or hesitate to call for military {naval) assistance.

The PRC is the well-identified threat to Taiwan. It is an easy guess that the great military potential so close to Taiwan, is causing the Taiwan military planners a severe headache. Lack of adequate and too few naval forces increase the problem further. The unstable situation in the China region is also causing a moral dilemma to many other countries that want to help Taiwan, but are faced with the economic realities of their commercial exploitation of the enormous Chinese market.

The strong Chinese fleet and its Air Force have both the range and precision in its weapons to threaten the Taiwan naval forces simultaneously on both sides of the Straits of Taiwan. We have to estimate that PRC units most likely have radar contact with all ships and aircraft over the whole Taiwan region. We also must assume that all Taiwan naval bases could be exposed to enemy air attacks within the hour from the outbreak of a conflict. But the PRC fleet can not handle a situation where it is faced with serious naval threat in joint operations from many directions along the whole East Coast of China.

A submarine force that can take the war to the enemy, tie up PRC naval escort and minesweeper resources and that could operate hidden from the Chinese air threat is therefore of key importance to the Taiwan Navy and of course a main threat to the PRC. Such a submarine force doesn’t have to include a lot of boats. I think that six to eight modern boats are enough to increase the PRC uncertainty. The possibilities of a Taiwan submarine war against the PRC coastal shipping are a serious threat to the PRC control of the nearest and most important waterways along the coast of China. Of course a Taiwan well-trained submarine force also could be an especially valuable asset in case a PRC invasion fleet starts to navigate across the Straits. Before such an invasion starts good intelligence, collected by Taiwan submarines, of the PRC force build up in the Chinese harbors is also of a high strategic value. The PRC desire to secure the control of these important waters will require well-trained and equipped naval forces that are able to work together in combined operations over a wide area. The Straits of Taiwan as well as the East Coast of China are very favorable for submarine warfare, so the PRC task is not an easy one.

The first operational factor to consider when looking at the Taiwan Straits from a submariner’s point of view, are the short transit distances to the operation areas. Within two to three days after sailing, a Taiwan submarine can safely be in its assigned area along the coast of China and from there collect important intelligence or establish a severe and long time submarine threat to the PRC possibilities to move its coastal shipping and naval forces.

The short ranges between the Taiwan bases and the Chinese mainland, also make it possible for the Taiwan submarines to operate in their assigned areas for considerably longer periods than for other navies in the vicinity with longer transit time to their operational areas. Naturally the demands on high transit speeds to reach the assigned areas in due time are also reduced.

At the same time the risks increase. It is difficult to find safe snorkelling areas free from shipping, enemy patrol areas (search areas) and airborne ASW. The limited geographic areas and short distances mean that large parts of the Straits of Taiwan can be under constant naval surveillance by coastal, ship and airborne radar systems. The risk of detection and danger close to the surface is therefore great. The Swedish solution to this problem has been to drive the technical development towards an operative AIP system based on the Stirling principles. Such a system allows the submarines to operate practically without snorting when on low speed in their assigned areas. Sweden is today one of few countries in the world with an operative non-nuclear air-independent propulsion.

The AIP system gives the CO the tactical flexibility he needs to penetrate in to the enemy’s coastal waters and to stay hidden for an extended period of time. My suggestion is that Taiwan seek a technical solution to this important tactical problem. Today the Stirling engine is the most favorable system. In the future the fuel cell will be a better solution due to the higher energy output.

The next factor to consider is the depth and other conditions of the sea in the area of operations. The depth in the straits and along the eastern coast of China is very shallow. To the Northeast, to the East and to the Southeast of Taiwan, there are great depths, and the deep water outside the continental shelf lies just some miles out from the Taiwan coast. Many submariners don’t like shallow water. They think that the boat can be trapped without any water to manoeuvre. That is partly true, but the shallow water also gives a lot of advantages to a boldly handled submarine. Normal spherical spreading does not exist in shallow waters, instead a channelling effect is the normal. That means that the energy is absorbed both in the seabed and in surface reflections, and that passive detection by using towed sonar arrays is very difficult due to the fact that the interesting low frequencies can’t spread because the wavelength is too great. A low or medium frequency active sonar has equally great difficulties to find a small target in the bottom reverberation. The limited depth causes reverberation between the bottom topography and the surface. The bottom also reduces the efficiency of depth charges, and an active homing antisubmarine torpedo will have severe problem to find the target and to discriminate it from the bottom reflections. The relatively flat muddy bottom gives few bottom bunces. High frequency sonar can detect a submarine sitting on the bottom, but the range is just measured in some hundred meters. For a submariner the knowledge and possibilities to avoid detection by utilising the whole water volume from the bottom to the surface are therefore essential for the survival of the boats. This demands a deep and thorough understanding of hydrography and hydroacoustics in the Straits of Taiwan.

But submarine command must also give the commanding officers the possibilities to utilise the depth and not hamper them by too short timeframes on the VLF traffic list. The information from the submarine command always has to be kept at a minimum just with the absolutely necessary signals. Timeframes too short have the results that the COs will be hugging to the dangerous surface to wait for radio signals instead of avoiding being detected and searching the depths for sonar contacts. Let the COs explore the depths-and they soon will be masters of the oceans.

I have already said that the eastern coast of China and the Straits of Taiwan are not deep. This creates good possibilities to avoid detection from long range sonar. But the shallowness increases the mine threat. During WW II, most of the Straits of Taiwan were declared dangerous for mines. The Japanese shipping hugged to the Chinese coast and took cover from the minefields in order to avoid the aggressive U.S. submarines. In a conflict between the PRC and Taiwan, I think that the mine threat in the area can be considerable. In sensitive areas, for example outside bases, harbours and at some choke points, where the shipping is channeled, the threat can be even more severe than in other places. The mine threat demands a good thorough knowledge of the differences in the earth’s magnetic field and an effective three-dimensional degassing system to minimize the magnetic signature of the boat.

The water surface temperature doesn’t vary much during the yearly seasons in the zone of tropics. The water is generally around and above 20 degrees Celsius. This factor creates a need for a battery cooling system, otherwise the battery will not give its maximum during extended submarine patrols. A system to circulate the battery acid is also favorable for increasing the time between snorting.

As a result of the relatively steady temperature, there is no large seasonal and geographical variation in the sound velocities. The possibilities to search for a rapid change of speed of sound to find cover is therefore limited. However on the Northeast and on the East Coast of Taiwan, where the water is deeper it is possible to find lower temperatures at depth.

I have a feeling that visual distance under water is quite low on the East Coast of China. This increases the difficulties in intelligence gathering.

To summarise; the East Coast of China and the Straits of Taiwan offers several opportunities for a submarine to avoid detection, and at the same time creates a severe submarine threat to the PRC possibilities to use the coastal shipping lanes.

Tactical and Operational Demands on a Taiwan Submarine

To stay hidden in such a hot area as the Straits of Taiwan, demands a very quiet submarine with long tactical and operational endurance and that the boat is equipped with modern sonar and other passive sensors. A variety of weapons such as torpedoes, mines and possibly ground anack missiles should be a strong requirement. Extremely good manoeuvrability will be needed in order to take full advantage of the shallow operational environment.

A modern submarine has several sensors. The big difference between Commander Fluckey’s and Commander 0 ‘Kane’s submarine war in 1944, and submarine operations today, is that the periscope (or radar on the surface as in the U.S. case) is no longer the primary sensor for surveillance. The periscope demands a tactic where the submarine has to work close to the surface while transmissions with radar reveal the presence of the submarine. The periscope can see to the horizon, maybe I 0 to 15 kilometres depending on height of target, periscope height, wave height and visibility. The periscope easily reveals the presence of the boat if not operated tactically correct-with short mast exposures, low mast height and with slow boat speed. Still the periscope doesn’t give that much information that it is worth the risk of being detected. Modern sonars can detect cavitating ships at distances five or ten times as long and is therefore the most desired sensor onboard.

Today there are many types of sonar that can be of great help for the CO, when fulfilling his important task to establish a severe and prolonged submarine threat to PRC. Low frequency passive sonar for long range detection together with LOFAR and DEMON technique will be of great help when establishing the surface picture. I think that a combination between Circular and Flank Array Sonar is the most favourable in the Taiwan area of operations. There is no need to install Towed Array Sonar due to the shallow water and that such sonar needs to be straight in the water to solve the bearing ambiguity. This creates a need for a tactic where the boat has to move at slow speed all the time. That consumes more energy than needed. High frequency sonar for mine avoidance is important when navigating in areas known or presumed to be dangerous because of mines.

Modern ESM with the antennas either in the periscope for close range work or in a separate mast add a lot to the intelligence gathering capabilities. Such a sensor is also of importance when establishing the surface and air threat picture in the area around the submarine.

The differences in the earth’s magnetic field have a significant importance to submarine warfare. Modern submarines are today protected by a degaussing system taking care of the three-dimensional magnetic field. The degaussing system is controlled through a sensor (probe) and a computer. The probe measures the magnetic field of the earth and the interaction from the submarine and automatically, by a computer, adjusts the current in the coils of the three-dimensional degaussing system. A good degaussing system decreases the risk of being detected by MAD systems and at the same time decreases the risk from magnetic bottom mines.

Submarines operating in mine infected waters have to face the risk that the boat causes a mine in the near vicinity to explode. Therefore such a submarine has to be designed to resist the shock from a standard mine-explosion at a distance quite close to the submarine. This is achieved by floating platforms where the crew and the important machinery are mounted on rubber mountings or steel springs.

I said earlier that the boat has to be quiet to be able to stay hidden in such a hot area as the Straits of Taiwan. The fight against noise transmitted from the submarine is a fight that never ends. The crew has to be well trained to understand what can be achieved with a quiet boat in terms of better own sonar performance and shorter enemy detection ranges. The crew must also be well aware that what has been achieved during months of hard work with technical innovations, can be destroyed in a minute by an uninterested crew member.

A look at the chart covering the East Coast of China reveals some places with geographical constraints-choke points-where the PRC shipping is naturally concentrated. Such choke points could provide a lot of targets and good possibilities for intelligence gathering. However the targets are normally escorted and therefore bold and skilled submarining is needed to get the job done. But with good passive sensors, long-range wire guided and homing torpedoes, it is often possible to hover, to sit at the bottom or to move very slowly, and still achieve a good reconnaissance or attacking position. This patient tactic saves energy and limits the time needed to recharge the batteries. It also enhances sonar performance and reduces the risk of detection.

A lockout capability for special operations has been more and more important in today’s submarines due to the high value of intelligence collected by Special Forces.

A weapon load with a mix of torpedoes, mines and surface to surface missiles can increase the COs choices a lot and at the same time, increasing the difficulties for PRC to predict how the Taiwan submarines will be used in case of an armed conflict.

A submarine operating in the Straits of Taiwan must be able to utilize the whole water volume. That means to be able to operate in depths of water that varies from just some 20-25 meters down to 300-400 meters east of Taiwan and also to operate from or close to the bottom to the surface.

The submarine therefore can use the background topography fully to its own advantage by operating as close as possible to the vertical or horizontal bottom, or try to be in a position on the bottom, but still be able to use its sensors and weapons.

This demands extremely good manoeuvrability both in the vertical and horizontal planes as well as a good weight compensat-ing system. The Swedish solution to this problem has been to design the boats with X-rudder configurations and a one-man steering console. The one helmsman operates both the compensat-ing water as well as the trim water and steers the boat in course and depth. This solution makes it possible to get a short turning radius and quick rudder reaction when operating near the bottom. For example it is no problem to go backwards with the submarine submerged. Due to the shape of the submarine’s hull and their rudder configuration, a turning radius less than the boats own length, can be achieved, in even at low speed. This is a desirable feature when operating in shallow waters near the bottom. The control-system makes it very easy for the one helmsman to control the submarine both in course and depth at the same time, regardless of the speed of the submarine.

A submarine designed to operate in shallow waters has to be designed and built to be able to safely hit the seabed at low speeds without sustaining any substantial damages. The X-rudder configuration mentioned above makes it possible to sit on the sea-bottom with very little risk of damaging the rudders and the propeller. The sonar arrays (even the flank array sonar) will continue to function even if the submarine is sitting on the bottom.

Another important factor to consider for a successful submarine warfare in the Taiwan water, is that a submarine is safer at sea than in the base area. The PRC have the capability to strike at the Taiwan naval bases from the air. In case of a higher tension in the area, I think it is of outmost importance that the Taiwan submarines immediately leave their normal bases. To spread the boats and possibly to sit on the bottom awaiting replenishment, is a better solution then to wait in the harbour for a PRC air raid. When the replenishment arrives, the submarine can surface and be at anchor when the replenishment comes by boat. This will support the need for a strong and flexible logistic support organisation, but it will pay off with a reduced threat against the valuable submarines. The Swedish solution has gone even further. Our submarines are capable of using the seabed while conducting repairs or recharging the main batteries between missions. The submarines own generators are capable of charging the main batteries to full capacity even with tow current in the later stages of the charging process. The submarines can be fully stored, including weapons, within one night, just by using small tenders.

When carefully considering the operational possibilities in the area around Taiwan, it is clear that a boldly and skillfully handled submarine will have many advantages over the ASW forces. There are technical solutions to overcome the problems with the shallow water and the absence of a protecting change in speed of sound. A submarine operated near the bottom will be extremely difficult to detect and attack by using sonar.

The conclusion is obvious, in view of the threats, that if a submarine is used in a correct tactical manner, the opportunities for submarine warfare are considerably better than the possibilities for successful ASW.


A strong submarine force can be the cornerstone in a new modern force structure for Taiwan. Modern submarines that can take the war to the enemy along the whole China coast, is very valuable and will create severe problems for the PRC to gain the necessary control at sea before the start of an invasion across the Straits of Taiwan. Such aggressive operational use of the subma-rines will also reduce the risk of a naval blockade against Taiwan because it will be dangerous for the major surface PRC ships to leave harbour. A change of operational concept forced upon PRC to a more defensive role will turn the tide in Taiwan favour. Modem submarines can change the whole strategic situation in the East China region in favour for Taiwan and its security policy. They are unpredictable in their operations and extremely difficult to detect and destroy. Modern submarines must therefore stand in the front of the Taiwan shopping list.

The East Coast of China and the Straits of Taiwan is very shallow. This is normally considered to be a strong negative factor for submarine warfare. I think that this is not the case for the Taiwan submarine force which in case of war needs to take the submarine war close to the enemy. The PRC has on paper a strong navy and submarine force. Many of the ships are of older origin and are originally not intended to operate in these shallow waters. But if they do, the PRC submarines are equally hard to detect and destroy for the Taiwan ASW forces. The PRC ASW forces are not well suited for shallow water ASW. The low and medium fre-quency sonar in those ships will not be to their advantage when operating in waters with an extremely high bottom reverberation. The modern PRC submarines of the Russian Kilo type are techni-cally advanced and quiet submarines. However they will have severe difficulties to detect small or medium sized submarines operating very shallow. As a result of my studies of the operational factors and the PRC ASW ships, I strongly recommend that the Taiwan submarine Force stay out of the deep waters east of Taiwan and concentrate its efforts along the coast of China. There are mainly two reasons for that. The PRC ASW forces will be better adapted to detect and destroy Taiwan submarines in the deep water and it will be much easier for Taiwan to find valuable targets on the coast of China. In case of higher tension in the area, I therefore recommend that Taiwan immediately establish a submarine threat along the East Coast of China. A closer study of the PRC weak points and valuable operative targets will be needed and will then give guidance concerning which areas to assign to the boats.

The shallow waters demand special technical solutions as mentioned earlier. The most important pan is to overcome the primary disadvantage of the conventional diesel electric submarine-the need to come to periscope depth to recharge the main batteries. This is a substantial tactical drawback especially in shallow and confined waters. Furthermore, continued advances in the development of airborne radar and infrared sensor capability, have increased the threat against a snorting submarine.

In order to reduce the time required to snort, and thereby improve the indiscretion ratio, the Swedish Navy has sought to identify an AIP technology that best suited our needs. In 1988 an AIP prototype system was installed in the Nackenclass (A 14) submarine for trials at sea. Subsequent tests, trials and refinements to the design resulted in the decision to install Stirling engine plants, in addition to the normal diesel engines, in all three of the new Gotland cJass (A 19) submarines (operative 1999). And recently a decision was taken to install the same type of machinery in two of the Vastergotland class (A 17).

By using AIP, the submarine commander can select his opera-tional profile. When the threat against the submarine is acute, the battery is used. For lesser threats, the AIP is used and with even lesser threats, the regular diesels are used while snorkelling. Today’s AIP system supplies sufficient energy to keep the battery loaded (floating the load) and still run the submarine at normal submarine speeds. This means that operating on AIP can cover 80-90 percent of the time in the patrol area. For greater speeds the battery is used and is automatically charged when the speed is reduced.

The Stirling system is inherently silent due to the fact that the combustion takes place in continuous and controlled manner. The low noise is further reduced by the double-elastic mounting arrangements and an acoustic hood reduces the airborne noise. In addition, the exhaust gas is let out into the sea in a controlled way through a unique arrangement that leaves, in practice, no trace of bubbles or heat.

An AIP capability improves the indiscretion ratio significantly. With Stirling engines onboard, underwater tactical endurance can be increased from a few days to several weeks. This supports an increase of operation times and minimises the time spent in base areas. But it also demands large stores of fuel, carbon dioxide absorbent, oxygen, supplies and/or auxiliary engines alongside the usual diesel-electric propulsion. An extended patrol time will increase the burden on the logistic support organisation.

Operations in the littorals also demand that the passive sensors give you a high bearing resolution in a multitarget environment (high background noise}. They should cover a large part of the frequency band to make it possible to avoid interference from strong active transmitters. Wide frequency coverage is also important for good recordings when collecting acoustic intelligence.

Other demands are the usual ones, when constructing and building submarines-low target strength, low noise level and an efficient degaussing system. The need to sit on the bottom now and then, is an important requirement. The x-rudder configuration and one-man steering console has been very reliable for Sweden.

The weapon development follows the construction of a modem submarine closely. I believe in a combination of heavy and lightweight torpedoes, mines and ground attack missiles. The Taiwan naval commanders have to have optimum flexibility when facing a multitarget c~isis. Flexibility in the submarines’ weapon load will increase the PRC uncertainty how the Taiwan boats will be used. That will increase the factors for success in case of an armed conflict.

Finally I am convinced that a strong modem Taiwan submarine Force of six to eight boats boldly operated in the shallow waters on the east coast of China can change the strategic situation in the east China region. Such a submarine force will increase the PRC uncertainty of Taiwan intentions and thereby tie up naval resources. This will minimise the risk of a PRC naval blockade as well as minimising the risk for an invasion across the shallow Straits of Taiwan.

Due to this fact, is it important that Taiwan continues to build strong naval relationships to countries that could provide the modern submarines and that could come to assistance in case of a conflict as well as a to give continued support in many fields of naval warfare. To identify a prospective submarine design and building country will be of outmost importance for the long-term security for Taiwan.

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