Military Embedded Systems

Unmanned underwater vehicles modernize U.S. Navy's sea-mine-hunting capabilities


April 23, 2014

Sally Cole

Senior Editor

Military Embedded Systems

Since the end of World War II, sea mines have damaged or sunk four times more U.S. Navy ships than all other types of attacks. In the future, advances in fully autonomous Unmanned Underwater Vehicles (UUVs) - equipped with embedded computing technology - will play a key role in sea-mine countermeasures.

Sea mines are deeply entrenched in the history of naval warfare, having played a significant role in every major conflict since the Civil War. So it’s no surprise the U.S. Navy has made the use of Unmanned Underwater Vehicles (UUVs) for sea-mine countermeasures a top priority.

An increased proliferation of inexpensive lethal threats targeting individual warfighters and high-value assets – combined with continued advances in computing, power and energy, sensors, robotics, and position-guidance technologies – is driving the push by the U.S. Navy to augment expensive manned systems with less expensive, fully autonomous unmanned systems.

Mines come in a wide assortment of flavors and types. During World War II, for example, mine threats ranged from advanced acoustic and pressure-influence devices to magnetic mines and electrical-potential/antenna-fired weapons. The four primary types of mines include bottom or “proud” mines that target submarines or ships in shallow water; moored mines held in place by anchors; floating mines assembled in buoyant cases and anchored; or buoyant drifting mines carried by currents and tides.

A relatively inexpensive sea mine, perhaps on the order of $10,000, is capable of sinking a ship worth more than $1 billion. “Much like Improvised Explosive Device [IED] use in Afghanistan or Iraq, sea mines play a similar role in making it difficult for an opposing force to move around or occupy an area without worrying that an unseen quiet threat can blow you up,” explains Frank Herr, head of the Office of Naval Research’s Ocean Battlespace Sensing Department (ONR; Arlington, VA;

Mines pose a huge challenge for the Navy, because this threat isn’t coming solely from new mines being laid in the ocean. “Tens of thousands of mines left over from World War II are on the seafloor and, since that time, more have been laid every decade by various nations,” notes Jeff Smith, chief operating officer for Bluefin Robotics Corp. (Quincy, MA;, a company that designs and builds UUVs – including the Knifefish.

Knifefish and its role in U.S. Navy mine countermeasures

Bluefin Robotics is working closely with General Dynamics Advanced Information Systems (Fairfax, VA;, the primary contractor of the Surface Mine Countermeasure UUV program, to develop Knifefish and modernize the Navy’s underwater mine-hunting capabilities.

Knifefish, a heavyweight-class specialized Bluefin-21 UUV, builds upon the low-frequency broadband acoustic payload technology initially developed by the Naval Research Laboratory to deliver a significant detection capability to the warfighter.

“Knifefish is a critical part of the Navy’s Littoral Combat Ship Mine Warfare mission package and will provide the fleet mine warfare commander and sailors with enhanced mine-hunting capability by addressing the Navy’s need to reliably detect and identify ‘proud’ and buried mines in high-clutter environments,” Smith says.

In terms of specs, a standard Bluefin-21 UUV is shaped like a torpedo, measures 21 inches in diameter and is 19 feet long (depending on its payload), weighs approximately 2,000 pounds, and is designed to operate to depths of 4,500 meters for 25 hours or more. Knifefish uses “a multitude of sensors to conduct its operations,” Smith says. “The vehicle’s main sensors include those typically found in UUVs, namely Inertial Navigation Systems (INS), Doppler-velocity logger, compasses, and sound-velocity sensors. Its payload is a low-frequency broadband synthetic aperture sonar for buried mine detection.”

To communicate, UUVs send brief messages to satellites. “We’ve been using Iridium, an over-the-horizon communication link, which enables communication with these research vehicles in the middle of the ocean without airplanes or ships,” says Herr. “But the Navy will use other communications channels for operations.” (See Figure 1.)


Figure 1: Knifefish communicates by sending brief messages to satellites. Courtesy of Bluefin Robotics Corp.

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Quite possibly one of the most important things to understand about UUVs is that these are not “drones.” These are autonomous systems; they aren’t remotely piloted. This fact makes their electronics and software extremely important. Knifefish is equipped with networking electronics, as well as communications, power-management, data-management, and storage electronics.

“Knifefish’s subsystems are based on an open architecture developed by Bluefin and General Dynamics Advanced Information Systems during the last decade,” explains Smith. “Its software uses a modular open systems architecture approach and is responsible for vehicle autonomy, mission planning and execution, payload data management, and other tasks.”

Because Knifefish has a modular design, it enables the integration of alternate payloads capable of addressing other applications and missions. While Knifefish is designed to fulfill the Navy’s requirements within the land-sea border known as the littoral zone, Bluefin has “variants of the Bluefin-21 tested for full ocean depth,” Smith notes.


Figure 2: Knifefish can detect and identify volume, bottom, and buried mines in high-clutter environments. Courtesy of Bluefin Robotics Corp.

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Knifefish will help the Navy to “reliably detect and identify volume, bottom, and buried mines in high-clutter environments,” says Tom Mason, senior program manager for General Dynamics Advanced Information Systems. “As part of the Littoral Combat Ship Mine Countermeasure mission package, Knifefish acts as an offboard sensor while the host ship stays safely outside the minefield boundaries – enhancing situational awareness and significantly reducing risks to Navy personnel.” (See Figure 2.)

Embedded computing and UUVs

UUVs like Knifefish are already quite advanced, but embedded computing can help take things to the next level. “Embedded computing will play a key role moving forward, because as computing continues to improve, these vehicles can become smarter,” says Herr.

Three levels of computing must evolve in order to achieve significant advances:

“A reliable and capable autonomous vehicle first requires a stable and well-characterized control system – a computer to act as the brains of the vehicle so the vehicle can operate itself. Second, it needs to be able to understand features in its environment, with programs to detect items and classify them specifically compared to other things – and to recognize that it’s not being spoofed to look like a mine – in an automated way,” explains Herr. “Third, it requires a separate set of software to control the vehicle so that it reacts appropriately to the physical (ocean currents) or tactical (detected targets) environment that it senses in its vicinity. In this way, it can search, avoid, or follow in an automated manner.”

Everything must become automated to avoid turning into “a big communications mess, with operators watching over the shoulder of a mission specialist, constantly asking ‘Is this what you’re looking for?’ To avoid this, we need it all on that vehicle, because we don’t have the communications bandwidth to get all of that information back to do real-time decision-making,” Herr notes.

Behavior defines UUVs, in terms of avoiding obstacles and moving in response to sensors in an automated way. “The vehicle itself needs to be under control, the sensing needs to be under control and automated, and the behavior of the vehicle – the interaction between the sensing and control systems of the vehicle – needs to be in a specialized software,” says Herr. “These three levels are what makes autonomy for these vehicles important and what it’ll take to separate it from a remotely piloted system.”

Open architectures

Clearly, one of the most vital components of a successful UUV program is its underlying architecture. “Designers and developers of UUV common-control systems must continue to evolve these solutions to be acceptable, flexible, and scalable to help agencies advance their missions,” Mason points out.

General Dynamics Advanced Information Systems’ unmanned mine countermeasure approach, which combines Commercial Off-The-Shelf (COTS) technologies and an open architecture, is driving innovation into the Navy’s mission to decrease costs and increase operational efficiencies. “Our open architecture enables quick configuration for ‘plug-and-play’ integration to evolve to meet current and future mission needs,” Mason adds.

The U.S. Navy’s current vision for UUVs “includes using multiple heterogeneous unmanned systems collaborating to reduce mission timelines,” says Smith. “A longer-term interest is to increase autonomy and energy for operational systems to effectively increase missions for greater persistence with less human intervention.”

To this end, ONR is seeking proposals for innovative technology solutions to enable unmanned surface vehicles capable of carrying out three phases of mine hunting: detection/classification, identification, and neutralization, all in a single sortie to potentially be integrated into a future Littoral Combat Ship Mine Countermeasure mission package. For more information, visit

In the future, any technologies that can increase reliability for UUV components will be important, according to Herr, such as development of lower-power payloads and other systems designed to extend battery life.

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