Needless to say, the Nazis had a crazy secret weapon for this
Back in World War II, nuclear propulsion wasn't an option. Nazi engineers instead experimented with chemically powered AIP, in their case the system developed by Professor Hellmuth Walter. Oxygen from air was replaced by the use of hydrogen peroxide, an explosive oxidiser sometimes used in torpedoes or rockets, burned together with fuel oil in a special turbine.
This system, in which an entire submarine was essentially converted into a highly dangerous explosive torpedo, offered impressive submerged speed but was hazardous and extremely troublesome to operate. It never saw frontline service, and was rejected after the war as making submarines - already very dangerous in those days - unacceptably unsafe. This decision was probably a wise one as even torpedoes using peroxide are a major hazard: it was a torpedo peroxide explosion which sank the Russian submarine Kursk in 2000, killing all 118 men aboard.
Nonetheless, ever since WWII, submariners unable to get hold of nuclear boats have aspired to some form of propulsion able to perform better than lacklustre batteries. AIP, like many much-discussed military wonder-weapons (electromagnetic pulse bombs, rayguns etc) has been just round the corner for decades. It has been particularly vigorously bigged-up as a threat by antisubmarine warfare specialists of the major Western navies since the Cold War ended and the threat of Soviet nuke subs largely vanished.
However, so far the only navies to deploy AIP have been friendly ones: Sweden has subs with auxiliary generators powered by Stirling-cycle engines (also sold to Japan) and the German and Italian navies have some boats with supplementary fuel-cell power.
DCNS in France, like other Western sub builders, have long offered an AIP option. In their case the use of extremely dangerous peroxide has been avoided in favour of only mildly dangerous compressed oxygen tanks, which allow a Rankine-cycle turbine alternator to run on alcohol fuel fully submerged - charging up the sub's batteries for greater endurance underwater. DCNS call this the "Mesma" system, and it is reportedly to be fitted to the last three Indian Scorpène boats.
Just when these will turn up is uncertain, however - the Indian Scorpène build is badly delayed and overbudget. Mesma boats are not now expected to come out of India's yards until 2018 or later.
The six new Indian subs announced this week are all, reportedly, to be fitted with AIP. Furthermore, two of these boats may be "imported from the foreign vendor directly" according to the Times' Indian government sources. If this happens the delays besetting the Scorpène project would perhaps be avoided and the Indian navy would become the first non-Western one to get working AIP.
Just what kind of AIP, however, is uncertain. While the Indian government has lined up the cash it is as yet unsure which foreign builder will get it. Reportedly Russia, Spain, France's DCNS and Germany's HDW are all in the running for a slice of India's $11bn.
AIP boats are generally held up as a terrible menace to Western naval dominance, especially by Western naval officers whose chances of career success depend on there being such a menace (or anyway, depend on measures being put in place to resist it).
Even so, there are reasons to stay calm even as it appears that AIP is finally spreading beyond friendly navies.
The AIP systems currently on offer, it should be emphasised, aren't an alternative to battery propulsion for high speeds. There's no option to use powerful AIP engines to turn a sub's screws directly as a Toyota Prius' engine can turn its wheels.
They have people starving in the country and keep going around other nations with the begging bowl and they waste it on submarines??
If you ask me we need to stop foreign aid to this country and look after out own.
India are one of the largest recipients of UK aid at over £1 billion pa.
They're spending $11 billion on these subs, have a next gen fighter project, nuclear weapons, a space program that plans to put an astronaut in space by 2015 and one of the fastest growing economies in the world.
Something is seriously not right.
Apart from the ongoing poor relations with Pakistan, India has an historic rivalry with China that has seen shooting wars happen. Given China's much larger nuke arsenal, it would seem a smart move for India to develop a sub-launched nuke option. An AIP sub with underwater-launched cruise missiles would be a lot harder for the Chinese to track and destroy, reducing the chances that a Chinese first strike would remove India's retaliatory capability. If India was dependent on siloed ballistic missiles alone, the Chinese could lauch an overwhelming attack that could knock out all India's missiles and the majority of the Indian air defence, then the Chinese Air Force could concetrate on hunting down any land-based cruise missile launchers. An unlikely event maybe, but the Indians might not want to bank on there never being another shooting war with India.
The same argument is used to justify our Trident subs as a better deterant than ICBMs - the Soviets could have feasibly launched a first strike against the limited number of European ballistic missile silos with a reasonable chance of success, but they can't guarantee to find our deep-diving, quiet, nuke subs, and just one sub could have removed a large chunk of Russian cities from the face of the Earth. Again, it was a highly unlikely scenario, even at the height of the Cold War, but we played safe and spent the billions (much more than the Indians). Whether we still need such a deterant is debateable.
/Come on, it's naval-related, just has to be S&Cs!