Nov 112013

AIP Technology Creates a New Undersea Threat

Inhanced performance of small, defensive submarines, a serious new underwater threat is developing in littoral waters. Increasingly, smaller nations unwilling or unable to accept the high cost of nuclear power to achieve greater underwater endurance and longer range are turning to lower-priced and less ambitious alternatives that still offer significant operational advantages over conventional diesel-electric submarines.

The Russian KILO, can remain submerged on battery at slow speed for periods on the order of three to five days. But now, several AIP schemes in development or already in operation can increase slow-speed range considerably. As interest mounts in “Air-Independent Propulsion” (AIP) for enhancing the low-speed endurance to as much as three weeks or a month. While still dwarfed by the potential of nuclear power, AIP offers diesel submarines a remarkable increase in capability

The Russian submarine manufacturing company, Rubin, is developing an air-independent propulsion (AIP) system [which will be available as a retrofit to the conventional diesel-powered KILO class submarines].

Closed-cycle Diesel Engines
Typically, a closed-cycle diesel (CCD) instal ation incorporates a standard diesel engine that can be operated in its conventional mode on the surface or while snorkeling. Underwater, however, it runs on an artificial atmosphere synthesized from stored oxygen, an inert gas (generally argon), and recycled exhaust products. The engine exhaust – largely carbon dioxide, nitrogen, and water vapor – is cooled, scrubbed, and separated into its constituents, with the argon recycled back to the intake manifold. The remaining exhaust gas is mixed with seawater and discharged overboard. Generally, the required oxygen is stored in liquid form – LOX – in cryogenic tanks.

China has two Type 636 submarines, the second of which joined the Chinese fleet in January 1999.

In September 2007, it was announced that Indonesia had placed an order for two Kilo Type 636 submarines, plus options to purchase up to eight more.

In November 2007, Venezuela signed a memorandum of understanding for three Type 636 submarines to be delivered from 2012 to 2013.

Type 636 is designed for anti-submarine warfare (ASW) and anti-surface-ship warfare (ASuW) and also for general reconnaissance and patrol missions. The Type 636 submarine is considered to be to be one of the quietest diesel submarines in the world. It is said to be capable of detecting an enemy submarine at a range three to four times greater than it can be detected itself.

The submarine has a launcher for eight Strela-3 or Igla surface-to-air missiles. These missiles are manufactured by the Fakel Design Bureau, Kaliningrad. Strela-3 (NATO Designation SA-N-8 Gremlin) has a cooled infrared seeker and 2kg warhead. Maximum range is 6km.

The vessels can be fitted with the Novator Club-S (SS-N-27) cruise missile system which fires the 3M-54E1 anti-ship missile. Range is 220km with 450kg high-explosive warhead.


The submarine is equipped with six 533mm forward torpedo tubes situated in the nose of the submarine and carries 18 torpedoes with six in the torpedo tubes and 12 stored on the racks. Alternatively the torpedo tubes can deploy 24 mines.

Two torpedo tubes are designed for firing remote-controlled torpedoes with a very high accuracy. The computer-controlled torpedo system is provided with a quick-loading device. The first salvo is fired within two minutes and the second within five minutes.

As near as I can tell, at this point most of the above listed submarines are conventional diesel. Not that that is much of a handicap, since these subs are used primarily for littoral defense, not long range blue-water offense.

Since the USS Nautilus, nuclear subs have always held the public’s attention. However, it was two Russian Foxtrot class diesel subs which came frighteningly close to setting off nuclear devices during the Cuban Missile Crisis. The first link below is about the Cuban incident. The second link has details about the Foxtrot class and, incredibly the third link invites you to visit a Foxtrot as a tourist attraction in the U.S.!


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