Three upgraded Agosta-90b class subs with MESMA engines serve in the Pakistani Navy. In the 1990s, submarines powered by Air Independent Propulsion (AIP) technology entered operational use. However, it should be kept in mind that even nuclear submarines rarely operate at maximum speed because of the additional noise produced. The contemporary U.S. Virginia class attack submarine costs $2.6 billion dollars, and the earlier Los Angeles class before it around $2 billion in inflation-adjusted dollars. Having ruled out a nuclear design, Australia will return to some form of conventional submarine that, like the Collins, uses diesel engines to charge batteries which in turn power motors for propulsion. They are the queens on the chessboard, the strategic game-changers. "But I guess that was pretty good because I otherwise still would have been down there.". Kevin Rudd's 2009 defence white paper promised to build a dozen of these killers to replace the trouble-plagued Collins-class fleet of six. You can't be sure there isn't one sitting quietly off your own coast or waiting in hiding to sink your ships. They may also have heavier armament, such as Vertical Launch Systems, when compared to most AIP powered vessels. One Swedish journalist aboard the submarine who was reportedly put ashore before the boat ran into trouble has not yet been accounted for, according to Danish newspaper Berlingske. While some conventional submarines can handle the distance, none have comparable underwater endurance. That means a big submarine with a big crew that can range far and wide and stay at sea for months. Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. There is also the question of the industry ''valley of death''. ''This is about sovereignty - our sovereign ability to have the submarine that does what we demand of it … so that when we put the crew into danger, we really do understand what we're doing. Proper naval submarines tend to operate at these levels, and the 18-metre Nautilus is far smaller than those. The smart money seems to be on the evolved Collins. The Nautilus itself was launched in 2008, having been built by Madsen and a group of friends. project to raise $50,000 for a refit fell well short of its target. ''But it's right up there with our biggest ever national undertakings, along with the Olympics, the Harbour Bridge and the Snowy scheme.''. In fact, nuclear-powered submarines may be unable to detect each other using passive sonar, as evidenced by the 2009 collision of a British and French nuclear ballistic missile submarines, both oblivious to the presence of the other. The submarine was rammed while it was carrying out underwater trials off Provincetown, Massachusetts. By comparison, AIP powered submarines have generally cost between $200 and $600 million, meaning a country could easily buy three or four medium-sized AIP submarines instead of one nuclear attack submarine. While her theoretical crush depth is given as "400m-500m", this seems a tad optimistic. The Swedes, for their part, have developed  four different classes of Stirling-powered submarines. Nuclear-powered submarines have traditionally held a decisive edge in endurance, stealth and speed over cheaper diesel submarines. The traditional size and hull form of submarines is driven by their need to carry armaments, sensors and a crew to operate them; the size is simply not necessary when you don't need half a dozen torpedo tubes in the bows and stern of your boat, or a ballistic missile compartment in the middle of it. Bloomberg News reported that Madsen told a local TV station about the sinking, revealing that a problem with a ballast tank caused the crowdfunded vessel to sink. AIP submarines have narrowed the gap, however. Nuclear submarines can operate underwater for three or four months at a time and cross oceans with ease. ''It's not a one-off, stop-start project. Nuclear reactors are quieter, don’t consume air, and produce greater power output, allowing nuclear submarines to remain submerged for months instead of days while traveling at higher speeds under water. You can't be sure there isn't one sitting quietly off your own coast or waiting in hiding to sink your ships. Bear in mind, however, that the AIP submarines are mostly small or medium sized vessels with crews of around 30 and 60 respectively, while nuclear submarines are often larger with crews of 100 or more. While AIP vessels may not be able to do everything a nuclear submarine can, having a larger fleet of submarines would be very useful in hunting opposing ships and submarines for control of the seas. Around fifty more are on order or being constructed. He currently writes on security and military history for War Is Boring. The Wikipedia entry for the boat appears to have been written by someone familiar with the Nautilus's design and systems, judging by the level of detail. By the time the 12th submarine is finished, it will be time to start looking for a replacement fleet. A few years ago a crowdfunding project to raise $50,000 for a refit fell well short of its target. That includes how to work with other countries, whose help we will inevitably need in designing the new submarine. Japan for her part has eight medium-sized Soryu class submarines that also use Stirling engines, with 15 more planned for or under construction. The industry association, the South Australian Defence Teaming Centre, this week welcomed minister Johnston's apparent preference for the evolved Collins on the ground that work would start sooner. While the navy apparently found the Nautilus and her captain, Peter Madsen, on the sea's surface, it appears that the boat foundered shortly afterwards as a result of "technical problems", judging by other accounts. As you read this, three Collins are at sea, which meets the benchmark for 50per cent of the fleet being operational at a given time. The rule of thumb, says Moffitt, is that a submarine can stay at sea for about a day for each crew member on board. ''It's going to be hard. That's a success. By comparison, the German Type 214’s maximum submerged speed of 23 miles per hour is typical of AIP submarines. And while we won't be designing everything ourselves, we will need the expertise to oversee and integrate all the work, says Rowan Moffitt - that means a generation of naval architects, systems engineers and systems integration experts. The 33-ton diesel-electric boat, UC3 Nautilus, is said to have foundered after getting into difficulty in Køge Bay, around 25 miles southwest of Copenhagen.. In 2004, the US Navy leased a Swedish Navy submarine, the Gotland, for one year of dissimilar training, and got more than t bargained for. Then there are intelligence missions - submarines are good for sitting quietly and listening, but only if they have the range and endurance to travel far and wide. It will be a further 18 months before the new government decides which of the two leading design options to go with, during which Australians can expect to hear much more furious argument. ASPI's Davies calls it ''sort of a no-brainer''. However, there’s reason to believe that AIP submarines can, if properly designed, swim underwater even more quietly. The problem is that such a combustion engine is inherently quite noisy and runs on air—a commodity in limited supply on an underwater vehicle. If Australia were threatened, it could use its long-range submarines to launch land-attack cruise missiles at the aggressor's homeland.