An almost universal trend in the design of diesel-electric submarines is that they are getting larger.  This can be observed in regional navies as diverse as those of Japan, South Korea, Singapore and Australia.  What they all have in common is a requirement for their submarines to be increasingly capable – particularly in overall combat power, range and endurance.  They are also all professionally led, high technology forces with close ties to the USN.

Republic of Korea Submarine Lee Sun Sin (Chang Bogo class) comes alongside Diamantina Pier at Fleet Base West, Western Australia, to take part in Exercise Pacific Reach 2019. (CoA / Yuri Ramsey)

South Korea is a particularly clear example. It was only in the 1980s that the Republic of Korea (RoK) Navy clearly identified a need for submarines to be part of the inventory.  This was driven mainly by an increasingly well-equipped and belligerent North Korea – at that time backed by both the USSR and China – but also by a desire to achieve a degree of parity with Japan.  The RoK embarked on a 30-year journey beginning with relatively small defensive submarines and culminating in a fleet that will soon be able to carry out a variety of missions at long range, defend extensive sea lines of communication and also able to conduct strategic strike against heavily defended targets.

Selecting Germany’s HDW as a long-term partner, the first RoK submarines – apart from several experimental submersibles – were the Chang Bogo class that first entered service in 1993 under the KSS-I program.  These were a derivative of the proven but limited Type 209, displacing around 1,300 tonnes submerged.  The first of these was built in Germany and the remaining eight in South Korea, mainly from imported kits with limited local content.

The next KSS-II generation were significantly larger and more capable at 1,860 tonnes in the form of the Sohn Wonjil class – 50% larger than their predecessor, giving them greater range and endurance as well as increased combat power through the ability to launch cruise missiles as well as torpedoes.  These were largely constructed in the RoK.

The current third generation KSS-III Dosan Anh Chango submarines are twice as large again at 3,700 tonnes.  The first of class is undergoing sea trials and is even more powerful with a vertical launch missile cell as well as conventional horizontal torpedo tubes, air independent propulsion (AIP), lithium ion batteries, and advanced combat and communications suites, to name but some of the features. They are entirely built in the RoK with local content of more than 70%, which is at the upper range of what can realistically be expected for a conventional submarine – a figure made possible by a relatively large production run of nine submarines.

HMAS Farncomb (Collins class) prepares to berth alongside its home port of Fleet Base West, Western Australia. (CoA / Kylie Jagiello)

Australia is another case in point.   In the 1970s the Royal Australian Navy acquired six Oberon class submarines from the UK with a submerged displacement of 2,400 tonnes; the current Swedish designed Collins class are 3,400 tonnes – and the future French designed Attack class are predicted to come in at just under 5,000 tonnes. However, all three types have comparable range and endurance figures – 20,000km and 60 days at sea.

In other words, the Attack class are twice the size of the Oberons but will not go much further – so the increase in size is explained by the vastly greater amount of equipment carried – particularly the combat system and weapons – and the variety of missions the new submarines will need to conduct.  Unusually for a new class of large submarine, at least the first three in the Attack series will be without AIP and will continue to use lead acid batteries.

Another major regional submarine user is Japan, whose designs seem to have plateaued at just over the 4,000 tonne submerged displacement mark.  This appears to be the size of the current Taigei class, which is being built even before the construction run of the preceding Soryu class (4,200 tonnes) has finished – which is visible evidence of the urgency of Japan’s naval buildup driven by Chinese aggression.  The preceding Oyashio class were also about this size – but they were a step change larger than the 1990’s Harushio class that started at 2,750 tonnes and during construction batches increased to 3,200 tonnes.  In a pattern similar to Australia’s the range and endurance requirements for Japanese submarines has not altered in the last 30 years, but their increasing size fits the pattern of growth driven by payload.

Factors driving this inevitable size increase include:

  • The need for greater range and endurance. In an increasingly multi-polar world threat scenarios are becoming more complex and alliance operations more frequent. As well as carry out offensive operations, sea lines of communication need to be protected. As countries increase the exploitation of seabed resources such as offshore oil and gas, these need to be protected – as do vital undersea communications cables;
  • A larger number of missions are now required. While submarines have often been required to perform roles in addition to firing torpedoes, now they need to conduct missions such as: long range land strike; communications and signals intelligence; special forces deployment and recover; and acting as a “mother ship” for increasingly numerous and capable uninhabited undersea vehicles (USVs);
  • The larger the submarine, the larger the sonar arrays that can be carried – particularly as conformal designs become more prevalent. These add enormously to both the combat power and intelligence gathering capabilities of submarines;
  • Crew habitability. This is often overlooked, but if navies in advanced countries want to attract the best and brightest then they need to provide a reasonable level of comfort for those on board, with missions now often in the 30-50 day duration. Modern, large diesel electric submarines with high levels of automation are a considerable improvement over their smaller, cramped, coastal predecessors;
  • Greater weapon load, particularly with missiles now being added to the mix of what can be carried to sea;
  • The need to have AIP that greatly increases the submarine’s underwater endurance. Without AIP a submarine will generally have to come to the surface every day or so and run the diesel generators to recharge the main battery pack. With AIP a submarine can remain underwater – and therefore almost impossible to detect for two or so weeks.

As phenomenal as all of these improvements are, they are expensive – for reasons that should be self-evident.  Just as submarines are increasing in displacement, so too is the cost of acquiring them.  Escalated for inflation, a small coastal submarine of around 1,200 tonnes could be acquired for US $500 – $800 million.  A second-generation longer-range boat between $800 and $1.2 billion.  The newest designs incorporating all of the performance improvements noted above but have a higher price tag – though this varies enormously on factors such as whether the cost of weapons is included and whether the submarine has all of the advanced features described or only some of them.

While some smaller coastal submarines are still being built – for example Indonesia’s 1,400 tonne Cakra and Nagapsa classes from South Korea – these are very much the exception to the rule.  Most navies prefer the mission flexibility that comes with designs in the 2,000 – 4,000 tonne category and the advanced electronics and large weapon loads that they can carry.  They obviously come at greater cost – but since submarines can be considered the capital ships of the 21st century it is a financial burden that most Governments believe is worthwhile.


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Kym Bergmann is the editor for Asia Pacific Defence Reporter (APDR) and Defence Review Asia (DRA). He has more than 25 years of experience in journalism and the defence industry. After graduating with honours from the Australian National University, he joined Capital 7 television, holding several positions including foreign news editor and chief political correspondent. During that time he also wrote for Business Review Weekly, undertaking analysis of various defence matters.After two years on the staff of a federal minister, he moved to the defence industry and held senior positions in several companies, including Blohm+Voss, Thales, Celsius and Saab. In 1997 he was one of two Australians selected for the Thomson CSF 'Preparation for Senior Management' MBA course. He has also worked as a consultant for a number of companies including Raytheon, Tenix and others. He has served on the boards of Thomson Sintra Pacific and Saab Pacific.


  1. Lead batteries! I believe we are the only country in the world building a new submarine with this type of battery! The Navies answer was “ it is proven technology”.
    Has anyone told them there are other batteries that are proven technology?

    • I believe you are correct in that even navies not currently using them are at least actively considering them. It’s interesting that Naval group say that their next generation conventional submarine will have lithium ion batteries.

    • The Victoria class are very old – re-badged Upholder class built in the UK in the early 1990s probably before lithium ion batteries were even thought of for submarine use.


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