August 26, 2014

Agni 6 (Agni VI) Why would India want to develop a 10,000 km Range ICBM?

The white lines represent the 10,000 km range (with a 500kg warhead?) of an Agni 6 (Agni VI) ICBM. The minimum and main Indian objective is the ability for at least one Agni 6 to deploy 3 tonnes of warheads from one missile onto Chinese northeast coast cities. The inner red circle is the 4,000 km range (with one tonne warhead?) of an Agni 4 (Agni IV) which may be operational in 2017. India's now operational Agni 3 (Agni III) can just reach Beijing with one 500 kg (no MIRV yet) warhead.

The flight of the 3 booster-stage Agni 6 with several MIRVs. Note that chaff might also be released to confuse anti-missle defence sensors including radar and perhaps satellite electro-optical.

Agni 6 (Agni VI)'s likely specifications are total weight 55,000 kgs, height 17-20 meters, 1.1 - 2.0 metre diameter, 3 stage rocket boosted. Launched from semi-hidden transporter erector launcher (TEL) truck, or disguised rail car. 

The short answer to "Why would India want to develop a 10,000 km Range ICBM?" is India may  develop ICBMs each able to launch several  warheads (MIRVs) (all up weighing 3 tonnes) capable of reaching northeast China - around 4,000 km from central India.

A basic law of physics is that due to gravity and momentum there is an inverse relationship between the weight of a warhead and the range of a missile. If the same rocket boosters (better with a slower burning propellant) for the heavy load were used for a light load, amounting to one 500kg warhead, then the range of that warhead may be 10,000 km.

Ranges involve capabilities even if India has no intentions about friendly countries. The 10,000 km range would bring the capitals of three of the other major nuclear powers into range. Such a long range increases flexibility, important for deterrence. For political reasons India probably does not wish to talk about longer range ICBMs - with 13,000 km capable of reaching all nuclear powers.

India has a right to defend itself. Having nuclear missiles with equal capabilities to the missiles of other great powers is important.

India wishes the 10,000 km range missile, known as the Agni 6 (Agni VI), to have characteristics equal to (parity with) the latest ICBMs of India's main nuclear opponent, China. China's latest ICBM under development is the DF-41 (Dongfeng-41) which will have the range to hit any capital of its nuclear opponents, including London and Washington DC. A December 2014 report indicated that China conducted the full test of the DF-41 involving MIRVs The DF-41 has an estimated range of 12,000km and “can carry up to 10 warheads, which separate from the rocket body during the final, third stage of flight and target individual cities. The military has previously carried out tests of the DF-41 but these probably involved only a single warhead”.

10,000 km range would also allow India to target SSBNs or warships (especially China's) attempting to hide as far out as the southern Indian Ocean and central Pacific Ocean. This is assuming India develops ICBM guidance systems (like China's DF-21D) against warships and submarines. India would wish that its Agni 6 would have at least the range of China's JL-2 SLBM (currently estimated as 8,000 kms).

The Agni 6 will be an evolutionary development of the Agni series of long range Indian ballistic missiles developed following the test of India's first nuclear device (1974).

Carrying multiple warheads (10 is the usual upper limit) on one missile is the most economical way to deploy warheads and such a deployment is more difficult to defeat with anti-missile defences. These multiple warheads are known as Multiple Independently Targetable Re-entry Vehicles (MIRVs). Along with live warheads light decoys can be carried (to draw off some anti-missile missiles) and various types of "chaff" (to confuse radar defences).

Agni 6  may be first tested in 2017 . Testing may last 4 years to 2021. Then in-service, operational around 2023 or later.

If India has developed fusion boosted fission weapons (like Joe-4) the yield of a single warhead missile may be up to 400 kT). If India has developed two-stage thermonuclear weapons - then each MIRV warhead may well have a yield between 100 to 250kt.

Cross reference this article with many concerning the Agni series including:

The Second Agni 5 Test, Any MIRV? September 16, 2013

China's, India's and Pakistan's Future Nuclear Rivalry August 12, 2013

Indian Strategic Weapons Programs - Gradual Progress, July 3, 2013

Agni 5's First Test in April 2012, April 27, 2012


August 24, 2014

India's Plans for 21 More Subs including SSNs

India financed the completion of INS Chakra (a Russian Akula 2) above - is long leasing it - and commissioned it into the Indian Navy in 2012. It is likely any Indian built SSN would draw heavily on Akula 2 technology with Russian assistance. See Pete's comment below.

Hindustan Shipyard (Visakhapatnam) - referred to in article below.

Mazagon Dock (Mumbai). - referred to in article below. 

Also see:

-  India's Rising Nuclear and Conventional Submarine Force, May 21, 2015 and

 -  South Asian Submarine Issues, December 7, 2014 concerning the construction of India's emerging SSBN base at INS Varsha on the East coast below Visakhapatnam. 


Rajat Pandit in the Times of India article below is overly gullible in accepting that India can deploy substantially more submarines in the short-medium term. There are plans to launch two more Arihant class SSBN in the next few years, but very little detail about SSN plans and very tentative SSK completion plans. Plans include:

- 6 Scorpenes for Project-75 Scorpene (with indigenous DRDO AIP) contracts signed in 2005-2006. Little observable progress since.

- 6 Project-75I (for India) (with AIP and land attack missiles) selection process continued through 2007 to present day for Indian construction SSKs designed in Spain, Russia, France or Germany. Little observable progress.

Arihant class SSBNs (including INS Arihant launched in 2009. Within this class:
   = S-1 is the half submarine reactor test rig at Kalpakkam (India's southeast coast, just south of Chennai)
   = S-2 is INS Arihant itself (undergoing trials - may never be operational).
   = S-3 is INS Aridhaman (under construction at Shipbuilding Centre Vadodara (India's west coast, north of Mumbai) or Shipbuilding Centre Visakhapatnam (east coast) prior to launch perhaps in 2015)
   = S-4 no name yet (under construction Shipbuilding Centre Vadodara prior to launch perhaps in 2016)

- 6 (yes 6) SSNs - to be constructed at Visakhapatnam. Few details, no date milestones. This very old FAS report indicates India has been interested in building or buying 6 SSNs since the 1950s, with Russian assistance, for fleet protection, mainly against Chinese subs. India financed the completion of INS Chakra (ex Nerpa) (a Russian Akula 2) - is long leasing it - and commissioned it into the Indian Navy in 2012. Since commissing Chakra has been almost invisable. It may not be operational but rather a full test model for examination and trials by the India Navy, DRDO and India's nuclear reactor sector. It is likely any Indian built SSN would draw heavily on Akula 2 technology and be built with Russian assistance.

The gullible Times of India, July 14, 2014, article follows :

"Move to fast-track two submarine projects gathers steam"

NEW DELHI: There is finally some urgency [words require deeds] being shown to rescue India's ageing and depleting underwater combat arm. The approval for two long-pending projects, one for construction of six advanced diesel-electric submarines and the other for six nuclear-powered ones, is well on the cards now.

Sources said the finance ministry has asked the defence ministry to "club" the separate projects to "draft a single note" for the requisite nod from Cabinet Committee on Security (CCS). "The two projects have been languishing for long in the files being exchanged between the two ministries. The government seems serious about fast-track approvals this time," said a source.

The approvals, when they come, will not be a day too soon since India is down to just 13 old diesel-electric submarines, barely half of which are operational at any given time, and a single nuclear-propelled submarine INS Chakra on lease from Russia without any long-range missiles.

It takes at least seven to eight years for the first submarine to roll out once its construction project actually gets underway. The two projects will together entail a cost of well over Rs 1 lakh crore spread over 10-15 years.

'Project-75India' for the six conventional submarines, armed with both land-attack missiles and air-independent propulsion (AIP) for greater underwater endurance, was granted "acceptance of necessity'' in November 2007, as was reported earlier by TOI.

But the global tender to select the foreign collaborator for it is yet to be even issued. As per the existing plan, the first two submarines will be imported to save time, while three will be constructed at Mazagon Docks (Mumbai), and the sixth at Hindustan Shipyard (Visakhapatnam).

The project to build the six SSNs (nuclear-powered attack submarines, usually without nuclear-tipped missiles), in turn, is to be undertaken at the secretive ship-building centre (SBC) at [Visakhapatnam]. India's first three SSBNs (nuclear-powered submarines with nuclear ballistic missiles) are already being built at the SBC to complete the country's nuclear weapons triad - the capability to fire nukes from land, air and underwater. The expertise gained in the construction of the SSBNs will help the SSN project, said sources.

The first SSBN, the 6,000-tonne INS Arihant, is slated to go for extensive sea trials soon after its miniature 83 mw pressurized light-water reactor, which went "critical" in August last year, attains "full power" in another month or so. The second, INS Aridhaman, is also to be "launched into water" soon with its hull and basic structure ready.

China, incidentally, has five nuclear and 51 conventional submarines. It is poised to induct up to five JIN-class SSBNs, with their new 7,400-km range JL-2 missiles, over the next few years.

India, however, has miserably failed in this arena. It was in 1999 that the CCS had approved a 30-year submarine-building plan, which envisaged induction of 12 new submarines by 2012, followed by another dozen by 2030.

But 15 years later, not a single new submarine has been inducted because of politico-bureaucratic apathy. The first programme, Project-75, was finalized only in 2005 to build six French Scorpene submarines at MDL. It's already running over four years behind schedule, with the first Scorpene now slated for delivery by November 2016 and the other five rolling out thereafter every 8-10 months. Moreover, the Rs 1,800 crore contract to buy 98 heavy-weight torpedoes to arm the submarines is also yet to be inked."

Also see South Asian Submarine Issues, December 7, 2014 concerning increasing Chinese submarine issues in the Indian Ocean. 


August 21, 2014

More of INS Arihant Revealed - Strategic Update

Revealed on August 20, 2014 is INS Arihant's conventional sail, supporting diving planes, The sail is similar to US Ohio Class and Russian Delta class SSBNs. The small hump for SLBMs aft of Arihant's sail indicates a limited missile carrying capacity underlining Arihant's main role as an experimental testbed rather than being a fully armed SSBN. 

Information is mainly drawn from and my knowledge of Indian subs since 2009 with many previous articles on this blog concerning Arihant..

Published on August 20, 2014 is the first clear image of INS Arihant, India's first indigenous nuclear-powered submarine. It may initially be armed with 12 750km-range K-15 (Bo-5) SLBM or four larger K-4s with a 3,500km range. The image above is a still from this NDTV news report .
Arihant is the first of a class of three nuclear-powered ballistic missile submarines with a displacement of 6,000 tonnes. Arihant has a Indian-Russian designed-and-built 83MW pressurized water reactor. 
This earlier image on this blog after Arihant was launched on July 26, 2009, gave little away (being highly touched up). Whereas the above photo clearly shows the distinctive 'hump' aft of the sail, where the ballistic missiles will be housed. The sail looks very similar to the sail of Russian Delta class SSBNs. Arihant appears to have a much better integrated missile hump than the Deltas and China's Type 094 SSBN.

The performance of SSBNs are critical for strategic stability in the region. If an SSBN is noisy (as the 094  presumably is) it will be easy to track. Excessive noise may not provide assured second-strike capability against an adversary. If Arihant is initially armed only with relatively short-range weapons such as the 750km K-15 missile, it would need to operate dangerously close to Pakistan's or China's home waters, thus making Arihant vulnerable to ASW resources. Arihant would be especially vulnerable if it has to move through narrow straits, like the Strait of Malacca, to get to Chinese waters. The longer-range K-4 missile has been tested from an undersea platform but is years from being operationally deployed on Arihant.

The nuclear sub design evolutionary process was particularly difficult for the US, Russia and China involving many test nuclear subs. As the UK and France received direct or indirect assistance from the US their evolutionary stages were far briefer involving fewer test subs. Much of the money India paid to Russia to modernise India's other nuclear submarine INS Chakra (the ex Russian Nerpa SSN) was for Chakra. But much of that money has also cross-subsidised Russian assistance to accelerate Arihant's development. A good strategy.
Like other key strategic weapons systems, Arihant is being jointly developed by the Indian Armed Services and India's Defence Research and Development Organisation (DRDO). It is highly likely that Russian advisers are assisting with Arihant's development (especially with the reactor and also SLBM launch  techniques).

Connect this Arihant article with the first Arihant article (INS Arihant Launched July 26, 2009 ) written on this blog days after Arihant was launched.


August 18, 2014

Navy SEAL and Submarine Capabilities

SEALs with rather thermal looking gear.
No submarine (from SSKs, SSNs to SSGNs) would be complete without the ability to carry a SEAL Team. US SEAL Teamscommonly known as the Navy SEALs, are the US Navy's principal special operations force and a part of the Naval Special Warfare Command and United States Special Operations Command. "SEAL" is only the US term while there are other foreign terms. Submarines can carry various SEAL dry decks shelters and vehicles of various sizes and missions. 

The SEAL acronym stands for Sea, Air, and Land, which identifies the elements in which they operate. SEALs work in small units -- often one to two men, but sometimes in a platoon comprised of up to 16. Two 8 man SEAL delivery vehicles (SDVs) could therefore carry one platoon. They are trained to perform specific tasks under any type of circumstance and in any environment. 
Missions fall into five main categories:
·    Unconventional Warfare (UW) - Using guerilla warfare tactics in battle. 
·    Foreign Internal Defense (FID) - Training given to foreign nationals in order to build relationships..
·    Direct Action (DA) - Moving against an enemy target. This may include assaults on land- or water-based targets, hostage rescues, ambushes, etc.
·    Counterterrorism (CT) - Includes direct action against terrorist operations, counter-terrorist actions for preventing terrorist acts, and protecting citizens and troops.
·    Special Reconnaissance (SR) - Includes conducting preliminary surveys to gather information, manning observation posts, and other types of surveillance, both overt and covert, where the goal is to gather information. This may include gathering hydrographic data (beach and water surveys) for landings or following an enemy unit and reporting its position.
The above categories overlap when it comes to actual missions, but these are the basis of SEAL training: to be expert in the skills required to perform these various tasks.

The object on the USS Dallas SSN submarine's back, known as the dry deck shelter, can deploy and recover free swimming SEAL divers and SEAL delivery vehicles (SDV) like the one pictured, while remaining submerged.

An SDV being maneuvered into one of the two dry deck shelters on the submarine's back.

Model of the inside of an SDV indicating it can carry as many as 8 SEALs. reported on August 1, 2014

Climb Into the Mini-Sub Navy SEALs Use to Bring Death From Below

Here’s the scenario: After suiting up with diving knives and silenced assault rifles, a team of three Navy SEALs on a submarine prepare to head to shore for a sneak attack. They put on their scuba gear and climb into a [SEAL Delivery Vehicle (SDV) that is shaped like a fat torpedo and]  not much bigger than a shower. Powered by a single rear propeller, it deploys from the [dry decks shelters of the] host submarine. After hours of slow, calculated movement through water too shallow for any submarine, radar indicates the SEALs have reached shore. Still underwater, they slide back the top canopy of their vessel and swim the last stretch to the beach under cover of night.

The key tool here is the SEAL Delivery Vehicle (SDV), the modern version of what’s essentially a tube with a propeller stuck on the back. It can be as compact as needed, sized to fit just one Navy SEAL or as many as [eight]. These craft are typically “free-flooding” vessels, which means they’re filled with water [which avoids most of the problems of buoyancy and center of gravity maintenance]. The soldiers inside breathe through their own scuba tanks or from on-board oxygen reservoirs...

The idea of a scaled-down, maneuverable submarine has been around for decades. Full-sized subs can’t operate properly in water shallower than 50 feet, so getting covert forces from ship to shore is tricky. Going in with scuba gear may require more oxygen than can be contained in a normal tank, and swimming in flippers for that long can leave even a hardened SEAL too exhausted to perform the mission.

Back in World War II, the British [Royal Navy (RN) Special Boat Service (SBS)] made a vehicle called the “submersible canoe,” or “sleeping beauty.” Soldiers trained with it and ran test missions, but it never saw live combat.

[Italy boasts the world's most successful record for SEAL/diver delivery vehicle operations. In World War Two Italy's Decima Flottiglia MAS (10th Assault Vehicle Flotilla") used manned torpedoes (known as SLC "maiales" "pigs") to destroy 72,190 tons of Allied warships and 130,572 tons of Allied merchant ships. Italians from the flotilla sank 2 Royal Navy battleships HMS Valiant, and HMS Queen Elizabeth (both of which, after months of work, were refloated and returned to action), wrecked the heavy cruiser HMS York and the destroyer HMS Eridge, damaged the destroyer HMS Jervis and sank or damaged 20 merchant ships including supply ships and tankers. Truly amazing!]

 In the early 1970s, US small craft were used off the coast of North Vietnam for combat and reconnaissance. One, the Mark VII, was built with a fiberglass hull and components made with non-ferrous metals, to minimize the craft’s radar signature. Power to the rear propeller came from two rechargeable silver-zinc batteries.

As the vessels now used by SEALs evolved, updates included Doppler navigation systems, sonar, and docking systems that reunited the unit with its host submarine once its occupants have filed out. A dry dock shelter lets soldiers move from the sub to the water, then get into the vessel.

The modern version of these “underwater swimmers” was officially commissioned in 1983 by the Naval Special Warfare SEAL Delivery Vehicle Teams. The then-new Mark VIII, which succeeded the Mark VII in the early 1980s, was designed to be much larger than its predecessors so it could move more cargo and more personnel, propelled by rechargeable batteries. The Mark VIII and its successors saw combat in Operation Desert Storm, and were used to secure offshore oil terminals during the most recent Iraq war.
 Above is a human "Torpedo SEAL" developed in the 1980s which is very similar to the highly successful WWII Italian "maiale" "pigs" human torpedoes. The Torpedo SEAL, is made by James Fisher Defence. The vessel, which is not currently used by the US Navy, can be deployed from a NATO-standard 533mm torpedo tube, or air-dropped from a helicopter. Propulsion comes from a lithium polymer battery that gets it to a top speed of 4 knots, or just under 5 mph. 

JF Defence says its “deliveries [are] often named as non-disclosed,” but that their six-man SEAL Carrier (above) "has been delivered to Sweden’s Navy" [according to]. The SEAL Carrier operates in three modes; surface, semi-submerged and submerged. Launched from a surface ship, SEAL Carrier vehicles can transit at speeds of up to 30kts on the surface before switching to submerged mode for a covert final approach.

The most recent variation on the SDV is the new the Shallow Water Combat Submersible (SWCS). Alabama-based Teledyne Brown Engineering won the $383 million contract in 2011 to design and build this new craft. We called them up, but Teledyne “respectfully decline[d] the opportunity to be interviewed.” They must be doing something cool." ENDS


August 11, 2014

Toward Stealth and Sea Denial: Submarine Modernization in East Asia

What technology might Singapore's 218SGs incorporate: fuel cell or Stirling AIP, Vertical Multi-Purpose Lock (VMPL) or Lithium-ion batteries? (Diagram courtesy of Globalsecurity)

The following is another excellent article* by Michael Raska, Research Fellow, Institute of Defence and Strategic Studies, S. Rajaratnam School of International Studies (RSIS), Nanyang Technological University, Singapore. The article details competition involving ever larger, more numerous and more capable submarines in Northeast and Southeast Asia. 

I maintain that Australia will need to respond to this strategic submarine competition be acquiring a new class of larger SSKs or more prudently SSNs. This is in recognition that only SSNs can perform all the roles required of a modern submarine force. 

Michael Raska's article was published by RSIS on July 7, 2014 in html at and also in pdf at

Toward Stealth and Sea Denial: Submarine Modernization in East Asia

IDSS / RSIS / Commentaries / East Asia and Asia Pacific / International Politics and Security / Maritime Security
07 JULY, 2014

RSIS Commentary No. 130/2014


An important aspect of the regional “arms competition” in East Asia is the gradual introduction of new classes of conventionally-powered diesel-electric submarines (SSKs), which are increasingly becoming “platforms of choice” – as force-multipliers in diverse missions as well as against superior forces.


Notwithstanding East Asia’s economic growth rates and deepening integration into the global economy, the region’s strategic realities reflect contending trajectories. As China expands its national interests in the broader context of “new historic missions”, it seeks to regain a great power status and reassert its geopolitical role in the region. As a result of China’s accelerating military modernization, regional powers are responding by revamping their force modernization priorities, alliances, and overall strategic choices.

The economic, political, and military rise of China, embedded in three decades of relentless Chinese economic growth, has propelled progressive modernization of the Chinese military with major improvements in virtually every capability domain.

China’s Naval Modernization and Submarine Expansion

Notwithstanding weaknesses and limitations in capabilities integration, China’s PLA Navy (PLAN) is gradually transforming toward a regional [blue water] defensive and offensive type navy with extended so-called anti-access/area-denial (A2/AD) capabilities, limited expeditionary capabilities, and corresponding defensive and offensive air power. China calls its comprehensive A2/AD strategy a “counter-intervention”, which is interpreted as denying the U.S. and its allies the freedom of action in China’s ‘near seas’ by restricting their deployments into theatre (anti access) and denying them freedom of movement there (area denial).

An important aspect of China’s multilayered strategy is the gradual introduction of new classes of submarines – both nuclear and conventional. China is currently operating as many as 45 submarines structured in six different classes: two classes of indigenously designed diesel submarines, including the Song class (Type 039) and the Yuan-class (Type 041), and four nuclear classes that include the Shang-class (Type 093), Jin-class (Type 094) nuclear powered ballistic missile submarines (SSBN) and the follow-on Type 095 nuclear-powered attack submarine (SSN) and Tang-class (Type 096) SSBN.
Since 2004, China is believed to have launched 12 Type 041 Yuan-class conventional submarines, which have been progressively modified to carry more advanced high-frequency sonar, upgraded weapons systems, noise reduction and air independent propulsion (AIP) technologies. The PLA Navy may procure up to 20 additional Yuan-class submarines based on technologies imported from Russian boats. Since the mid-1990s, China has procured as many as 12 Kilo-class submarines from Russia, and is reportedly negotiating the purchase of at least four fourth-generation Amur (Lada)-class or possibly a fifth-generation Kalina-class, both featuring advanced AIP systems.

Regional Responses

In Northeast Asia, Japan and South Korea are prioritizing the procurement of new types of submarines. In September 2013, South Korea launched a fourth 1,800 ton Son Won-ill class (German Type 214) submarine, featuring AIP and combat management systems. South Korea now operates 13 submarines: nine Type 209 Chang Bogo and four Son Won-ill class submarines. Meanwhile, in October 2013, the Japan Marine Self Defense Force (MSDF) launched its newest submarine the Kokuryu – the sixth of planned ten Soryu class boats first commissioned in 2009. With its range, endurance, sensors, weapons load and other systems, including the Stirling AIP propulsion system and Harpoon anti-ship missiles, the Soryu class is regarded as the most advanced in Japan’s conventional submarine fleet of 16 submarines.

In Southeast Asia, the relatively high acquisition costs and maintenance requirements have traditionally precluded a quantitative diffusion of submarines. However, the recent introduction of more capable coastal diesel-powered submarines provides unprecedented capabilities. Most recently, Vietnam received two of six Kilo-class (Project 636) diesel-electric submarines from Russia in 2013- 2014, designed for diverse reconnaissance and patrol, anti-submarine and anti-ship missions.

Indonesia, Malaysia, and Singapore are also planning to expand or upgrade their submarine fleets. From 2007-09, Malaysia took formal delivery of two French-built Scorpene-class submarines, equipped with underwater-launched Exocet anti-ship missiles. Both submarines are based at the Kota Kinabalu Naval Base in Sabah, East Malaysia, indicating their primary mission to protect Malaysia’s sovereignty in part of South China Sea. Meanwhile, Indonesia has ambitious plans to expand its submarine fleet to at least six, and ideally to 12 by 2024, a key element in the “Minimum Essential Force” (MEF) and declared goal of developing a ‘green-water’ navy. In 2012, the Indonesian Navy (TNI-AL) announced a US$1.1 billion contract for three Type-209/1400 diesel-electric submarines, constructed by South Korea’s Daewoo Shipbuilding and Marine Engineering.

In November 2013, Singapore announced a contract with German shipbuilder ThyssenKrupp to acquire two advanced Type-218SG submarines that will augment existing Archer-class boats and replace ageing ex-Swedish Challenger-class by 2020. Type-218SG, designed for littoral, shallow sea operations, is a customized design that will integrate features from Type 214 and possibly Type-216 ‘concept submarine’ fitted with fuel-cell AIP system. [Pete's Comment - the atypical 218 designation might also suggest that the 218s might be fitted with Stirling engine AIP in line with the Stirlings already incorporated into Singapore's two Archer class subs.]

Strategic Ramifications

Over the past decade, the operational utility of submarines in East Asia has widened: from anti-submarine warfare to force protection such as close submarine escort missions, intelligence surveillance, and reconnaissance (ISR), support of Special Forces, and other complementary deterrence and defensive tasks supporting territorial defense. At the same time, the introduction of submarine-launched anti-ship and land-attack cruise missiles, anti-submarine sensors and weapons, as well as air independent propulsion systems have increased their stealth capacity to remain undetected shortened their target-identification-and-attack cycle, and ultimately, improved their flexibility, mobility, endurance, reach, and lethality.

For smaller, defensively-oriented navies in East and Southeast Asia, these attributes enable “sea-denial” capabilities aimed at preventing an opponent from using the sea, rather than providing a degree of sea control to use the sea for own power projection. Submarines will therefore become an increasingly valuable strategic asset in the region, particularly with installed AIP systems. The key difference, however, will be in the experience, training, and skill set of its operators."

Michael Raska's earlier submarine article appeared on this blog on July 31, 2014 as Air Independent Propulsion - A Game Changer .

August 5, 2014

Air independent propulsion (AIP) Technologies and Selection

See a more generalised Submarine Matters discussion on why a country may or may not want AIP at Air Independent Propulsion (AIP) Issues of April 23, 2015.

If Australia selected an air independent propulsion (AIP) technology for conventional diesel-electric submarines it would be on a new-construction Future Submarine rather than being retrofitted to the current Collins subs.

Much of the following information draws on Australian Dr Carlo Kopp’s article originally published in Defence Today, December 2010. Much information is also drawn from Edward C. Whitman’s article with some major updating.

Some AIP Attributes When Selecting

In assessing the merits of any AIP system several factors, which include potential weaknesses, are important, including:

• Submerged endurance achievable with an Australian specified profile, comprising specific segments of submerged operation at specific speeds and depths, representative of real missions;
• Suitability of the AIP to Pacific, Indian and Southern Ocean operating environment as distinct from the North Atlantic-Baltic operating environments of most AIP builders;
• Acoustic signature contribution produced by the AIP system in specific operating regimes, but especially at varying speeds and depths;
• Vulnerability of the AIP systems (especially hydrogen or oxygen storage) to near miss explosive or implosive effects that otherwise not lethal to the submarine or its systems;
• Various failure modes of the AIP system and its oxidiser/fuel storage, and to what extent are these repairable if a failure or battle damage arise in a contested patrol area;
• Failover modes and internal redundancy in the AIP system, and what ‘casualty’ modes exist if a catastrophic failure arises to get the boat out of danger;
• Replenishment options (if any) of oxidiser and fuel from a tender when operating at large distances from a friendly port;
• Up-front costs of AIP systems in dollar amounts and as a portion of the total cost of the sub;
• Lifecycle cost of operating and maintaining the AIP system, at a representative operational-tempo.

In the final analysis, any AIP system will need to be subjected to some representative and tough testing before it even makes a shortlist (which may rule out the Russian and Spanish technologies which are only at a developmental stage). This is because AIP is becoming a mission critical single point of failure for the submarine in a combat environment. If the AIP system fails for whatever reason while the submarine is operating in a contested area, it may not have the option of snorkelling home.

The strength of AIP includes it being very quiet. More than two weeks submerged with a submarine immobile or moving slowly. AIP extends operating range but cannot drive the submarine at anything over low speed for medium to long ranges. Can AIP be seen as a form of backup if specific portions of the diesel-electric drive-train fail?

AIP Technologies

These are arranged by what I consider the likelihood that Australia might select a foreign company and/or submarine which utilises that technology.

Hydrogen-oxygen fuel cell system. (Diagram courtesy of )

See Type 212/214 Fuel cell PEM AIP on bottom submarine (diagram courtesy of this site)

Fuel cell systems – German PEM

Fuel cell - PEM AIP is likely if Germany’s TKMS is selected to build Australia’s Future Submarine.

Operation - Fuel cell based AIP systems typically employ a hydrogen oxygen fuel cell to generate electrical current, which then powers the boat’s systems. The principal issue in operating any fuel cell based system is the manner in which the oxygen and hydrogen are stored (physically and chemically) prior to introduction into the fuel cell. The available technology is the Polymer Electrolyte Membrane (PEM) cell used in the Siemens SINAVY AIP fuel cell modules.

The oxygen supply is stored as LOX in the PEM system. The hydrogen propellant supply in the PEM system is described as via “reformer gas” in some documents, or solid metal hydride in others. The former scheme typically involves the decomposition of a hydrocarbon fuel to generate hydrogen. The fuel cell can operate by recharging the subs batteries or in the case of the PEM directly feed the electric motor. The fuel cell produces distilled water as a waste product.

Strengths - A virtual absence of moving parts, except small pumps, which makes this AIP exceptionally quiet in terms of machinery noise and cheaper and easier to maintain compared to other AIP technologies. The PEM fuel cell only operates at 80 ° C reducing heat signature and cooling problems. PEM is relatively efficient 70% of energy (on what measure? Of LOX?), because the fuel cell directly feeding the electric motor. PEM has been successfully incorporated into many German Navy and export submarines.

Weaknesses - Fuel cells have a relatively high up front cost. Fuel cells are relatively difficult and expensive to retrofit or cannot be retrofitted? Does PEM AIP generally produce less average power than Stirling or MESMA? Is there less “dash speed” in an emergency? The process of storing and replacing on board hydrogen and LOX involves significant safety hazards.

More Details - Fuel cells are employed in the German HDW built Type 212 (with nine 30-50 kW fuel cell units) and two 120 kW units are fitted on Dolphin class, on internationally marketed Type 214 subs and on some Type 209 mod subs.

It is unknown whether the two Type 218SG subs being built in Germany will utilise fuel cell PEM or Stirling engine AIP. If it is Stirling (an AIP Singapore is already familiar with in the two Archer class) then that might be one reason that the new submarines have been called "218" rather than "214".

Methanol defragmentor is the latest AIP being considered - German, France and Spain may be ahead in this.

Indian DRDO Fuel Cell - A March 2014 report indicated DCNS might install a DRDO developed AIP based on hydrogen fuel cell technology on one [or more] of the six Scorpenes beinge built at Mazagaon Dock under Indian Navy Project 75. This was in preference to an older version of French MESMA being offered for the Project 75 Scorpenes. The DRDO fuel cell might be also be built into the second line of Indian future conventional submarines under a different project, known as P75I.

Now Saab and FMV's Stirling AIP system.

Stirling-cycle heat engine with external combustion

 Stirling Engine

Stirling AIP is another strong contender for Australia’s Future Submarine if Japan’s Soryu drive-train or a direct purchase from Sweden (Saab) is selected.

In the Stirling cycle, heat from an outside source is transferred to an enclosed quantity of working fluid - generally an inert gas - and drives it through a repeating sequence of thermodynamic changes. By expanding the gas against a piston and then drawing it into a separate cooling chamber for subsequent compression, the heat from external combustion can be converted to mechanical work and then, in turn, to electricity. Like MESMA, this approach has an advantage over internal combustion systems, such as the closed cycle diesel (below) in that the combustion processes can be kept separate from those that actually convert heat to mechanical work. This provides significant flexibility in dealing with exhaust products and controlling noise.

The Swedish developed Stirling system employs LOX as the oxidiser and diesel as the fuel, which are combusted at a pressure higher than that of the surrounding water mass permitting the exhaust to be directly vented to sea. The Stirling engine is coupled to a generator that feeds into the boats’ primary electrical system.

Strengths - Stirling engine are relatively simple and less hazardess in that they just use diesel and oxygen with Stirling engines running on liquid oxygen and diesel oil to turn a generator to produce electricity to charge the sub's batteries. Stirling technology has been widely used by several navies including Sweden’s (current Södermanland and Gotland class), Singapore’s (two Archer class), Japan’s (Soryu class) and some Chinese PLAN SSKs.

Weaknesses – Its moving parts can contribute to noise. The Stirling engines operate at a pressure of 20 bars, which limits the submarine’s depth capability to 200 meters, unless an exhaust gas pressure intensifier mechanism is used. As with other AIP systems that burn LOX and diesel, the LOX supply is the principal constraint to achievable endurance.

More Details - On Sweden’s Gotland class subs there are two 75 kW Stirling engines for propulsion or charging batteries. The endurance of the 1,500-tonne boats is around 14 days at 5 knots (5.8 mph; 9.3 km/h). Japan’s Soryus (of the size and tonnage expected for Australia’s Future Submarine) utilise four 75 kW Kawasaki Kockums V4-275R Stirling engines

MESMA closed-cycle steam turbine

Closed cycle steam turbine - French "MESMA"

Closed cycle steam turbine AIP (French "MESMA") is likely if France’s DCNS is selected to build Australia’s Future Submarine.

Closed cycle steam turbine systems could be compared to nuclear systems, in that heat is used to generate steam, which via a turbine or turbo generator charges the batteries that power the electric motor. Stored oxygen allows the fuel to burn creating the heat.

DCNS in France offer the MESMA (Module d’Energie Sous-Marine Autonome) system in a lengthened Agosta or Scorpene class sub, requiring the insertion of a hull section about 8.3 metre long, weighing around 305 tonnes. The MESMA system burns ethanol, using stored LOX as the oxidiser. The propellant mix is burned at 60 atmospheres at up to 700 ° C, which imply a need for seawater cooling. DCNS claim up to three times the submerged endurance of the basic diesel-electric Scorpene class, or around 20 days.

Strengths – Relatively high output power is available. The design permits relatively easy? retrofitting into existing submarines by adding an extra hull section-plug.

Weaknesses - The hazards (like Fuel cells and Stirling) of storing and handling the liquid oxygen (LOX). While the MESMA may provide higher power output, its net efficiency might be the lowest (estimated at. 25%) as its rate of oxygen consumption is higher. The MESMA has significant moving parts, which may radiate detectable noise. Ultimately, the maintenance and crew training requirements of the MESMA steam turbine system are significant - adding to cost. The burning process yields exhaust carbon dioxide which needs to be expelled behind the sub at any depth perhaps making it vulnerable to advanced airborne and ASW ship sniffing sensors?

Offered by the French DCNS. MESMA has a relatively small customer base having only been retrofitted into some Pakistani Agosta class subs.

See a French DCNS announcement of a "second generation AIP" (more fuel cell type - not really a MESMA development) at DCNS' new submerged SSK solution - Lithium-ion battery and 2 AIPs of November 6, 2014.

The Spanish S-80's AIP - known (in Spanish) as Propulsion Independiente de aire. 

Spanish Bio-ethanol (or maybe Methanol) (Closed cycle steam turbine?)

Though Spain’s Bio-ethanol AIP technology is not fully tested and of course hasn’t been used in practice Australia has a counter-intuitive purchasing history of untried military technology. This would be in the context of Australia selecting the not fully tested or even deployed Navantia S-80 Isaac Peral class submarine.

The S-80 AIP technology under development is purportedly “completely different” from MESMA. The S-80's AIP system is based on a bioethanol-processor consisting of a reaction chamber and several intermediate Coprox reactors, that will transform the BioEtOH into high purity hydrogen. The output feeds a series of fuel cells. The Reformator is fed with bioethanol as fuel, and oxygen (stored as LOX) generating hydrogen and carbon dioxide as subproducts. The produced hydrogen and more oxygen is fed to the fuel cells.

The bioethanol-processor also produces a stream of highly concentrated carbon dioxide and other trace gases that are not burned completely during combustion. This gas flow is mixed with sea water in one or more ejector venturi scrubber and then through a CO2 Removal System and whose purpose is to dissolve the "bubbles" of CO2 in water to undetectable levels.

The oxygen and fuel flow rates are directly determined by the demand for power. The AIP power in the S-80 submarine is at least 300 kW. A permanent-magnet electric motor moves a fixed propeller of a special design, that doesn't create cavitations at high speed.

Weakness – Sounds highly complex. Cost unknown and cannot currently be estimated. Undeveloped. Unused even by the Spanish Navy. This problematic formula of claims may increase the chances of Australia selecting it.

Closed-cycle diesel engine (Diagram courtesy of )

Closed cycle diesel (CCD) systems

Australia almost definitely won’t buy this AIP system. indicates “CCD systems have been developed by a number of firms in Germany, Britain, the Netherlands, and a few other countries. However, except for a 300-horsepower demonstration system refitted onto the German Navy's ex-U 1 in [1992-] 1993, no modern CCD systems have entered naval service. England's Marconi Marine recently acquired CCD pioneer Carlton Deep Sea Systems and is marketing a CCD retrofit package for existing conventional submarines, such as South Korea's nine Type 209s. Although one key advantage of CCD systems is their relatively easy backfit into existing submarine engineering plants, there have been no takers. Despite the additional supply complication of needing regular replenishment of cryogenic oxygen and inert gas, there are logistics advantages in retaining standard diesel engines and using normal diesel fuel.”

Russian Kristall-27E AIP as it may appear on a yet to be developed Russian Amur-Lada-Kalina conventional submarine. (Sourced from here

Russian Kristall-27E AIP

Australia definitely won’t buy Russian.

Russia hopes that it could develop the 4th generation Lada-Amur class have been discontinued because Russia has been unable to develop satisfactory air independent propulsion (AIP). This makes prospects for an Amur class from dim to nil.

January 2016 reports from Russia are that Russian AIP (essential to market Lada or Amurs) has not been developed hence additional Ladas (after L2 and L3) and any export Amurs will no longer be built. Prospective Amur customers have probably been offered the existing Improved Kilo (636) class instead. This is assuming customers (other than China) would not accept a Russian offer of a future "fifth generation" Kalina class SSK - with the Kalinas only likely to be operational (with AIP) in the Russian and maybe Chinese Navy in the mid 2020s.

Russia is far behind Western countries in fully developing and actually deploying AIP systems. Russia has been talking about its untested Kristall-27E AIP for at least 12 years. 

Kristall is described as a system with alkali matrix electrolyte, intermetallid storage of hydrogen, cryogenic storage of oxygen and a low-temperature electrochemical generator.  See Kristall-27E AIP described in great detail here and here.

Strengths – None verifiable as yet.

Weaknesses – Its Russian - unpopular with the Australian military. All of this Russian originated description appears to be marketing claims in place of full development and deployment. It appears that Russia is not developing AIP for its own submarine corps but instead may develop it if foreign customers places orders for AIP submarines. The risk appears to lie with customers during a lengthy development phase. This may explain why customers have restricted their purchases to non-AIP Kilos - that are less expensive and less technically risky than AIP Amurs-Ladas. It will be interesting if the Kalinas sell - though we are talking years of development.

Nuclear reactor ("AIP") on submarine (Source - Excellent explanation of nuclear technology)

Nuclear Propulsion

While politically unpopular with Australia’s previous (Labor) Government nuclear power is the ultimate AIP as it presents no restrictions on submerged time, range or operation at a sub’s maximum speed.

Arguments like “we couldn’t train Australian nuclear technicians-engineers (or hire US-UK personnel) within 20 years to operate or maintain submarine reactors” appear to be poorly argued, but current, conventional wisdom.

For the usual safety reasons such Australian SSNs could be based at Fleet Base West, Rockingham, Western Australia which US SSGNs and SSNs already regularly visit.


Using any of the AIP technologies would involve lengthy selection processes. Extensive foreign and local training would be required for the technicians, engineers, officers, crew and officials required to maintain, use, administer and repair these technologies. All this takes years and in many cases decades. AIP technologies need to interact with the complete submarine weapons system - so can't only be seen or assessed in isolation.

Sources Used Include

Edward C. Whitman’s article 

The Submarine Research Center reference on AIP and U31 at