Sailors assigned to the submarine tender USS FRANK CABLE’s (AS 40) weapons department stabilise a MK48 torpedo during a weapons onload. FRANK CABLE is one of two forward-deployed submarine tenders in the US 7th Fleet area of operations and conducts maintenance and support of deployed US naval force submarines and surface vessels in the Indo-Asia-Pacific region.


Lockheed Martin’s Mk-48 heavyweight torpedo was introduced into the US Navy (USN) in 1972 and remains the primary ASuW and ASW weapon for USN attack submarines. It is optimised to attack major surface combatants as well as difficult to acquire (low acoustic profile, deep diving) submarines including ballistic missile boats. The currently deployed Mk-48 ADCAP (ADvanced CAPabilities) weighs 1,600 kg and is fired – like most but not all heavy torpedoes – from a standard 21-inch tube. The US Navy reports a speed in excess of 28 kn, a range of more than five miles, and an operational depth of more than 366 metres. The Mk-48 can be wire-guided or deployed in fire-and-forget mode. A digital proximity fuse determines the optimal time for detonation. The 295 kg warhead is designed to detonate beneath the target’s keel in order to break its back.

The weapon has been continually upgraded to enhance performance and to keep pace with adversarial countermeasures. The Mod 6 introduced in 2009 can remotely receive software updates while at sea. The latest iteration, the Mod 7 Common Broadband Advanced Sonar System  (CBASS) jointly developed with the Royal Australian Navy, is optimised for both blue water and littoral operations and has advanced counter-countermeasure capabilities. Key elements of the upgrade include a broadband analogue sonar receiver and an improved digital guidance and control system. The increased sonar bandwidth improves targeting and tracking capabilities against high-performance submarine and surface targets with low acoustic signatures. Similar or equivalent heavy torpedoes are produced in other nations, often with range and speed superior to the official capabilities of the Mk 48 although independent experts maintain that the USN significantly downplays the Mk-48’s performance, which they estimate to attain 55 kn attack speed and an operational depth between 800 and 1,300 metres.

Anti-Ship and Land-Attack Missiles

In addition to torpedoes, attack submarines can carry a variety of missiles to combat surface vessels, land targets, and even aircraft. Depending on the submarine class, missiles can be carried in dedicated cells embedded in the topside hull, or be carried in launch canisters and deployed via torpedo tube.

All attack submarine classes of the US Navy are outfitted with Vertical Launch System (VLS) cells carrying TOMAHAWK Land Attack Missiles (TLAM). A torpedo-tube launched variant of the 21-inch diameter cruise missile was sold to the UK in 2008. Depending on variant, TLAM range lies at 700 or 900 NM with a speed of 475 kn. Guidance options include GPS, INS, TERCOM (Terrain Contour Matching) and Digitised Scene Mapping Area Correlator (DSMAC). The TOMAHAWK is currently produced in the Block IV TLAM-E configuration, which adds the capability to reprogramme the missile while in-flight via two-way satellite communications to strike any of 15 pre-programmed alternate targets or redirect the missile to any Global Positioning System (GPS) target coordinates. The TLAM-C and -E variants carry a penetrating 455 kg high-explosive unitary warhead; the TLAM-D carries submunitions. The US Navy is currently developing a Maritime Strike TOMAHAWK as a long-range ASuW weapon; this weapon should achieve IOC with the surface fleet in 2021, with follow on deployment with the submarine fleet.

The US Navy has test fired two Raytheon-built TOMAHAWK cruise missiles from new submarine payload tubes on the VIRGINIA class USS NORTH DAKOTA (SSN- 784) for the first time in 2017. The tests proved the submarine’s ability to load, carry and vertically launch TOMAHAWK missiles from the new Block III VIRGINIA Payload Tube, the company announced, adding that the up graded tubes feature fewer parts and will be even more reliable. In addition to the new payload tubes, the US Navy is also developing a new VIRGINIA Payload Module. “The new modules will triple the number of TOMAHAWK missiles that VIRGINIA class submarines can carry, dramatically increasing each sub`s firepower,” Raytheon stated. “As the Navy continues to modernise its subs, Raytheon continues to modernise TOMAHAWK, keeping this one-of-a-kind weapon well ahead of the threat,” said Mike Jarrett, Raytheon Air Warfare Systems Vice President. “Today`s TOMAHAWK is a far cry from its predecessors and tomorrow’s missile will feature even more capability, giving our sailors the edge they need for decades to come.” The US Navy continues to upgrade the TOMAHAWK Block IV`s communications and navigation capabilities, while adding a multi-mode seeker so it can hit high-value moving targets at sea. These modernised TOMAHAWKs are on track to deploy from 2019.

Light Weight Wide Aperture Array (LWWAA) is the only available, passive, fibre-optic hull mounted sensor array in the market and is critical to the operation of the US Navy’s VIRGINIA Class fleet.

Fitting the LWWAA hardware for Block IV of the US Navy VIRGINIA Class submarines.

Sonar / Acoustic Sensors

Submarine sensors are utilised for navigation, for tactical situational awareness including locating and engaging hostile vessels and mines, and for conducting ISR (Intelligence, Surveillance and Reconnaissance) missions. They can be divided into acoustic (including sonar), optical and electromagnetic systems.

Acoustic sensors are divided into active and passive systems. Active sonar emits an acoustic pulse which rebounds when it strikes a solid surface; the returning signal or “echo” is received by the sonar’s transducer array and transferred to a signal processor for evaluation. Active sonar can determine the object’s contours (aiding classification); it can also determine its distance, direction and speed by measuring the time elapsed between pulse and echo. However, active sonar also reveals the presence of the searching submarine. Passive arrays send no signal, but merely monitor for sound from surface ships and submarines; such acoustic signals can include sound produced by ship’s engines, rotor wash, explosions, collisions or even heavy objects being dropped onto a deck. Passive acoustic monitoring alone cannot determine the distance to an object. However, triangulation between several sonars or sensors can allow even passive systems to calculate distance to a target.

Submarines carry several sonar systems simultaneously, with each being optimised for different tasks. These include bow and flank mounted sonars as well as towed sonar arrays which can be deployed as needed to augment the on-board systems; towed arrays have the advantage of less interference from sound generated by the host submarine.

The first ten units of the US Navy’s VIRGINIA class attack submarines introduced in 2004 featured a spherical bow sonar array enclosed in a dome-shaped cover. Similar arrays – the MTK 500 SKAT – are found on several Russian attack submarines including the new YASEN class. However, as of USS NORTH DAKOTA (the eleventh VIRGINIA class vessel) the USN switched to the horseshoe-shaped Large Aperture Bow (LAB). The LAB contains a medium-frequency active array and a passive array with improved performance over the previous transducers. The new transducers, adopted from the SEAWOLF class attack submarines, are designed to last the life of the submarine. And while the dome surrounding the spherical array was filled with air, requiring a complex system to maintain constant pressure, the dome surrounding the LAB is filled with water. Taken together, the transition to the LAB increases performance while reducing maintenance effort and expense.

On both flanks the VIRGINIA class is equipped with a fibre optic Light Weight Wide Aperture Array (LWWAA) consisting of three flat panels. High frequency active sonars are located at the chin and on the sail, serving for navigation, mine detection and ASW. A conformal high-frequency active sonar array on both sides of the sail provides sonar coverage of the waters above and behind the submarine, eliminating sensor blind spots. In addition to the hull mounted systems, the VIRGINIA class carries two towed passive arrays: the TB-34 to search for adversary submarines in cluttered littoral environments; and the TB-29 to detect, localise and pursue submarines in all environments. Technological advances are constantly incorporated as new submarines are built, and retroactively applied to older vessels after proving themselves. The newest VIRGINIA class submarine, USS SOUTH DAKOTA, will feature new large vertical sonar arrays on each flank. These passive arrays are expected to improve the submarine’s ability to detect other vessels well before being detected itself.

Traditionally, acoustic sensors have utilised ceramic hydrophones which require electronics and signal processing to be located near the sensor. Northrop Grumman has developed fibre optic sensors as an alternative. They are in service as part of the LWWAA on the VIRGINIA class. Acoustic pressure striking the sensor causes a malleable sensing spool (called a mandrel) to expand or contract, temporarily changing the flow of laser light through the optical fibre. That change is measured and transmitted to the signal processor located deep within the submarine. The fibre-optic system offers several advantages. The hydrophones are simpler, containing fewer parts than piezoceramic transducer systems – less than ten passive components and splices per channel, compared with hundreds per channel for ceramic arrays, according to Northrop Grumman. Data loss during transmission to the signal processor is reduced. Since they lack electronic components, they are also immune to electromagnetic interference.

Optical and Electromagnetic Sensors

Modern periscopes are equipped with high-definition cameras which can automatically switch to infrared or low-light mode as needed. A prime example is the Series 20 Attack Periscope produced by Safran. Despite the designation, it can also be used for ISR and navigation. It has multiple features including a gyrostabilised direct optical channel with 4 magnifications, a high-definition colour camera, an infrared camera, a low-light camera with anti-blooming, as well as enhanced image processing capabilities and video recording features. The periscope can be integrated with GPS and Electronic Warfare/Electronic Support Measures (EW/ESM) antennae.

The next evolution in optical sensors is the photonic (alternately: optronic) mast. In contrast to the periscope, which is raised and lowered through the hull and therefore constitutes a weak point in the submarine’s physical integrity, a photonic mast is stationary outside the hull. The VIRGINIA class was the first class to replace periscopes completely with photonic masts. The two KOLLMORGEN (now L-3 KEO/Calzoni) AN/BVS-1 masts feature high resolution electro-optical colour, black-and-white, and infrared cameras, low-light television and a laser rangefinder. The sensors are connected via optical fibre to three work stations (including the captain’s) in the command centre on the second deck. The workstations feature LCD screens which display the sensor images, and joysticks and keyboards to control the sensors. Streaming images are recorded on tape and CD for documentation and analysis. The British ASTUTE class which entered service in 2010 is also equipped with photonics masts, produced by Thales.

Electronic Warfare (EW) is now a major element of submarine operations. Electromagnetic sensors constitute a major element of a submarine’s ability to conduct Intelligence, Surveillance and Reconnaissance missions. Sail or mast mounted EW systems – such as the US Navy’s AN/BLQ-10 ESM system – can intercept and analyse radar and communications signals. Finally, radar also belongs to the submarines’ electromagnetic capabilities. Mast mounted radar is used when surfaced, for navigation and safety as well as for tactical situational awareness.

System Integration

Even the most powerful sonars and sensors are of limited value by themselves. The input from a submarine’s various component sensors must be aggregated in order to create a useful operational assessment. This is the role of command and control systems such as the Integrated Sensor Underwater System (ISUS) developed by Atlas Elektronik. The ISUS 100 Combat System for Submarines networks acoustic and non-acoustic sensors to create a unitary tactical picture. The system is modular, and can incorporate a variety of Atlas Elektronik sonars as well as periscopes, photonic masts, ESM and navigation radar, and even off-board sensor date supplied via data link. The aggregated data can flow through the target management system to the weapons control stations, creating an uninterrupted “sensor to shooter” chain for all onboard weapons including torpedoes, missiles and countermeasures.

Technology in a Future War at Sea

The incremental “speeding up” of naval warfare technologies-of reconnaissance, the speed of decision, the speed of movement, and the speed and accuracy of “fires”-will continue in the future. Looking forward into the twenty-first century, should American sea power confront a peer competitor, the environment will be contested in all physical domains of air, surface, subsurface, and space by faster and smarter technologies. Based on the American order of battle in the 2010s, the US Navy will likely seek to dominate in all domains and will still deploy predominantly manned systems in the near to medium term. as of late 2015, the US Navy continues to plan for large, manned machines, to include additional P-8 maritime surveillance aircraft, Gerald R. Ford-class carriers equipped with an electromagnetic aircraft Launch System, and two new classes of manned submarines. One, a “Block V” variant of current Virginia-class submarines, will have four vertical tubes capable of launching robots or divers; the other, an “Ohio replacement Submarine,” will have a significantly quieter propulsion system. Similarly, the F-18 attack and fighter variants will be followed by the manned Joint Strike Fighter.

Naval Special Warfare Command’s (NSWC) Teledyne Brown Shallow Water Combat Submersible (SWCS) and Lockheed Martin Dry Combat Submersible (DCS) programmes.

The first two SWCS boats were due to be delivered to NSWC later in 2017 with developmental testing ongoing. Concurrently, USSOCOM continues to operate a single DCS technology demonstrator in order to validate design, construction and commercial classing methods in terms of cost, as well as schedule and performance, sources added. An initial operating capability for the DCS concept is not expected to be in place with NSWC until 2020, it was added. Lockheed Martin and Submergence Group, who won the DCS contract in 2016, also has the option to build a further two additional DCS boats. Capable of being deployed from subsurface dry docks integrated on board US Navy `Ohio’ class nuclear powered ballistic missile submarines for example, the DCS is capable of covertly inserting and extracting Navy SEAL special forces teams to and from target areas, while also supporting live operations with command and control capabilities and potentially fire support. This programme is being supported by the navy’s Dry Deck Shelter (DDS) programme which could provide a similar capability to `Virginia’ class nuclear powered attack submarines. A request for proposals is expected to be published later in 2017, sources confirmed.

An August 20, 2014, blog post states:

The U. S. Navy is hard at work developing new underwater transports for its elite commandos. The SEALs expect the new craft-and improvements to large submarine “motherships” that will carry them-to be ready by the end of the decade.

SEALs have ridden in small submersibles to sneak into hostile territory for decades. For instance, the special operators reportedly used the vehicles to slip into Somalia and spy on terrorists in 2003.

Now the sailing branch is looking to buy two new kinds of mini-subs. While details are understandably scarce, the main difference between the two concepts appears to be the maximum range.

The Shallow Water Combat Submersible will haul six or more naval commandos across relatively short distances near the surface. The SWCS, which weighs approximately 10,000 pounds, will replace older Mark 8 Seal Delivery Vehicles, or SDVs.

The other sub, called the Dry Combat Submersible, will carry six individuals much farther and at greater depths. The most recent DCS prototype weighs almost 40,000 pounds and can travel up to 60 nautical miles while 190 feet below the waves. Commandos could get further into enemy territory or start out a safer distance away with this new vehicle. SEALs could also use this added range to escape any potential pursuers. Both new miniature craft will also be fully enclosed. The current SDVs are open to water and the passengers must wear full scuba gear-seen in the picture above.

In addition, the DCS appears to pick up where a previous craft, called the Advanced SEAL Delivery System, left off. The Pentagon canceled that project in 2006 because of significant cost overruns. But the Navy continued experimenting with the sole ASDS prototype for two more years. The whole effort finally came to a halt when the mini-sub was destroyed in an accidental fire.

Special Operations Command hopes to have the SWCS ready to go by 2017. SOCOM’s plan is to get the DCS in service by the end of the following year.

Underwater motherships

SOCOM and the sailing branch also want bigger submarines to carry these new minisubs closer to their targets. For decades now, attack and missile submarines have worked as motherships for the SEALs.

Eight Ohio- and Virginia-class subs currently are set up to carry the special Dry-Deck Shelter used to launch SDVs, according to a presentation at the Special Operations Forces Industry Conference in May.

The DDS units protect the specialized mini-subs inside an enclosed space. Individual divers also can come and go from the DDS airlocks.

The first-in-class USS Ohio-and her sisters Michigan, Florida and Georgia-carried ballistic missiles with nuclear warheads during the Cold War. The Navy had expected to retire the decades-old ships, but instead spent billions of dollars modifying them for new roles. Today they carry Tomahawk cruise missiles and SEALs.

The Virginias-Hawaii, Mississippi, New Hampshire, North Carolina and the future North Dakota-are newer. The Navy designed these attack submarines from the keel up to perform a variety of missions.

SOCOM projects that nine submersible motherships-including North Carolina as a backup-will be available by the end of the year.

The Navy has a pool of six shelters to share between the subs. SOCOM expects the DDS to still be in service in 2050.

But prototype DCS mini-subs cannot fit inside the current shelter design. As a result, a modernization program will stretch the DDS units by 50 inches, according to SOCOM’s briefing.

The project will also try to make it easier to launch undersea vehicles and get them back into the confines of the metal enclosure. Right now, divers must manually open and close the outside hatch to get the SDVs out.

Crews then have to drive the craft back into the shelter without any extra help at the end of a mission-underwater and likely in near-total darkness. The sailing branch wants to automate this process.

With any luck, the SEALs will have their new undersea chariots and the motherships to carry them ready before 2020.


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