The original stealth weapons, submarines may be second only to unmanned systems in the degree to which they have exploited new technology in the past two decades. Major advances have included air-independent propulsion (AIP) systems, increasing submerged endurance and mobility; automation, reducing crew size (and consequently, life-cycle costs) and improving habitability; electro-optical masts that can sweep the horizon with high-definition in seconds and drop out of sight; and new torpedoes and other weapons. On the near horizon is the the mating of SSKs with unmanned air and underwater vehicles (UUV).

One of the newest SSK designs in the world is the TKMS/Kockums A26, in development for the Swedish Navy and due to become operational late in the decade. The 1,800-ton A26 builds on experience with the Gotland class—which proved a headache for the U.S. Navy during two years of “aggressor” operations out of San Diego—and likewise uses Stirling-cycle AIP propulsion, with a submerged endurance of up to 18 days. (Kockums AIP technology is also used on Japan's 16SS.)

New features include a low radar-cross-section sail, an integrated tube-type “multimission portal” for swimmers and UUVs, and what the builder calls Genuine Holistic Stealth Technology (Ghost), giving the A26 lower sonar signatures across all bands than the Gotland. For example, noise and vibration isolation techniques are improved, including damping plates between hull frames. Airflow speeds in ducts are limited and cable and pipe turn radii are above set minima. The A26 has new features such as a smart degaussing system that uses external sensors to match the boat's magnetic signature to its background. It will be operated by a crew of 26.

TKMS' Howaldtswerke-Deutsche Werft (HDW) unit in Kiel, Germany, is also leading a two-year, $100 million upgrade of the Israeli navy's three Dolphin submarines at Israeli shipyards. Dolphin, Leviathan and Tekuma will be joined by two more subs, enhanced with AIP, under construction at HDW, while acquisition of a sixth is being negotiated.

The upgrade includes 10 launchers per boat for Rafael's Torbuster, a fourth-generation, hard-kill decoy that seduces incoming torpedoes using technology based on the Rafael's decoys for surface ships. Upon detection of an incoming torpedo, the sub releases the decoy from an external launcher, which propels itself to a safe distance before attracting the incoming torpedo by transmitting acoustic signals, using reactive acoustic deception.

Torbuster actively engages the torpedo as it closes in, activating an explosive warhead when the target is at the closest proximity, inflicting sufficient damage to the torpedo to neutralize it. The system is operated from a single console, a launcher control unit. The operator is able to monitor the decoys in the launchers, to follow and activate the launchers, and to control the system's safety interlocks and devices.

Another element of the upgrade is Rafael's Sea-Com, a hardened, secure, Internet protocol-based communications suite integrating internal voice, data and video communications, as well as external radio and satellite links. Sea-Com reduces sensor-to-shooter time through efficient collaboration of multidisciplinary systems and real-time access to information resources.

Russia's Project 636 SSK, called Kilo in the West, set standards in the Cold War, but its designer—St. Petersburg-based CDB Rubin—is now playing catch-up after years of underinvestment. Rubin's general director, Andrey Dyachkov, tells DTI that the company is completing bench-testing of a prototype AIP system.

The system is a hydrogen fuel cell, as used by TKMS-HDW, but instead of operating on stored hydrogen, it relies on chemical re- formation of the sub's diesel fuel, which eliminates special on-board tankage and hydrogen infrastructure on shore. According to Dyachkov, this technology has already been validated during AIP bench tests. “This allows us to use the standard diesel fuel and doesn't require complex ground support” compared to the German variant, he explained.

Rubin plans to install AIP in the Amur 1650, offered for the Indian navy's tender for six conventional submarines. An export version of Russia's Project 677 Lada class, Amur has a surface displacement of 1,765 metric tons, submerged speed of 19 kt. and a crew of 35. It is designed to strike both sea-based and fixed land-based targets. The 66-meter (217-ft.) boat carries six torpedo tubes and Klub-S (SS-N-27) missiles in 10 vertical launchers that can be fired in salvos. For the Indian tender it also will be equipped with Russo-Indian PJ-10 BrahMos supersonic missiles fired from the same launchers.

The AIP can be installed in the Amur 1650 in a separate module along with the conventional diesel-electric propulsion system. Using the AIP, the sub's endurance can increase by two or three more weeks from 45 days currently, based on a customer's request. Continuous submerged time increases from the current nine days to 14-20 days.

The first Project 677 boat, the St. Petersburg, is undergoing reliability testing with the Russian navy in the Baltic Sea. In 2012, it is expected to complete the testing of its sonar system, says Dyachkov. The Admiralty Shipyards in St. Petersburg are constructing two more, the Kronstadt and Sevastopol, but so far there are no funds for completing these with AIP.

Rubin plans to further increase Amur 1650 endurance by replacing lead-acid batteries with lithium-ion (Li-Ion) batteries. The designers do not report about their progress in this field, but say that lithium-ion batteries will be able to increase the sub's submerged endurance and distance by 50% at low noise patrol speed and threefold at full speed. Unlike the AIP, which is only compatible with the Amur, the new batteries can also be offered for Rubin's Project 636 Kilo boats.

Li-Ion batteries are a key feature of another radical new submarine, under development since 2008 by South Korea's Agency for Defense Development (ADD)—the new-technology 510-ton KSM-500A mini-sub.

South Korea has two 150-ton Dolgorae-class minis for special operations and ASW training, but as plans for a replacement have evolved, the requirements have expanded. From the outset, the new sub was intended to attack large surface units, and initial plans were for a 15-kt. speed, 2,000-nm range and two weeks of submerged endurance. The ADD explained that the speed was the minimum required to escape from a counterattack after firing torpedoes at major surface units, and the range covers operations into the coastal waters of potential adversaries. For underwater endurance, the ADD called for more than two weeks.

Then, the March 2010 sinking of the corvette Cheonan by a North Korean torpedo—most likely from a Yono-class midget submarine—brought the small-sub concept into the spotlight as a possible counter to the North's 70-strong sub fleet.

The latest concept, the KSM-500A, unveiled in October 2011, is even faster and has a three-week endurance. It carries six torpedoes—two 533-mm heavies to attack surface ships and four 324-mm lightweights to target submarines—plus a payload interface module that can hold missiles or mines. The craft is designed to carry 10 crew and up to seven combat swimmers.

The notable feature of the KSM-500A design is its propulsion, which is all-electric. By dispensing with diesel generators and relying on Li-Ion batteries with more than twice the energy density of lead-acid ones, the KSM-500A will both be “ultra-quiet” and able to sprint for greater distances above 10 kt. than current small submarines, the ADD claims. Packaging a motor, rotor, stator and propellers into an integrated motor-propulsor eliminates the drive shaft and makes room in the aft compartment for a payload module, while a flank-array sonar can extend over almost the whole length of the hull because there is no noisy machinery in the aft section. The KSM-500A concept is not yet frozen and a hybrid system, comprising an AIP unit and Li-Ion batteries, is still an option.

While lethality, survivability and mobility are still the focus of most design efforts, DCNS, the French military shipyard, recently completed the world's first study on the environmental impact of a submarine's life-cycle, seeking innovative ways to reduce this impact.

Eric Fusil, the study's leader, tells DTI that “in general when you improve the environmental impact your product also becomes more efficient in terms of functionality and cost. This has been the case with Sepia [Submarine with Environmental Performance Improvement Along-life], a name we chose with a nod and a wink to the Latin name of the common cuttlefish, famous for its excellent ability to camouflage.”

Sepia analyzed a submarine's damage to human health, ecosystems and natural resources depletion, and the solutions found—while maintaining the same strategic performances as a Scorpene submarine—save 160 tons of fuel a year, or 40%, and cut the global environmental impact by 35% while eliminating liquid and solid waste disposal at sea.

The team considered every step of the entire life cycle and every part of the ship, including packaging and related products such as consumables and electricity consumption on the construction site. They looked at the materials used, the manufacturing process, the period of active duty, maintenance and dismantling.

“All the solutions we chose were at least at a prototype stage,” says Fusil. The silicone hull coating, for example, already exists. It not only reduces drag but is also non-toxic for the organic matter (shells, etc.) which tries to latch onto the ship. “They can latch onto this surface for a short time, but it comes off in micro-particles, taking the matter with it,” explains Fusil.

The Sepia design has a shrouded propulsor and dual drive motors, a smaller one for patrol and a larger one for sprint. Li-Ion batteries would be used, helping reduce life-cycle diesel consumption by 40%.

With Christina Mackenzie in Paris and Bill Sweetman in Washington.