VESSEL REVIEW | Knifefish – US Navy tasks new underwater drones with minehunting in littoral waters

US technology firms General Dynamics Mission Systems (GDMS) and Bluefin Robotics recently delivered the first Knifefish surface mine countermeasure unmanned underwater vehicle (SMCM UUV) system under a contract awarded by the US Navy.

The contract, awarded in August 2019 immediately after approval was given to enter low-rate initial production (LRIP), calls for the procurement of five Knifefish systems – a total of 10 UUVs – and support equipment.

The UUVs were all designed using an open architecture concept that can be quickly and efficiently modified to accommodate a wide range of missions.

Designed for deployment off a littoral combat ship (LCS), Knifefish is primarily tasked with detecting, avoiding, and identifying mine threats, reducing the risk to personnel by operating in minefields as an off-board sensor while the host ship stays outside the minefield boundaries. The UUV may also be used to gather environmental data to provide intelligence support for other mine warfare systems.

The torpedo-shaped Knifefish was developed as a modified variant of a Bluefin Robotics UUV that was originally marketed to civilian customers for use in seabed surveys, marine salvage operations, and marine scientific exploration. It has a length of 19 feet (5.8 metres), a diameter of 1.75 feet (0.53 metres), and a displacement of 1,700 pounds (0.77 tonnes). An onboard lithium-ion battery generates enough electrical power to enable the craft to operate for up to 16 hours before it needs to return to the mothership.

The mine detection equipment consists of a low-frequency broadband synthetic aperture sonar and a computer that can store locations of detected mines and "mine-like" objects. Although many of its details remain classified, the system is so advanced that it can even detect mines that are buried on the seafloor and that would otherwise escape detection by less capable equipment.

The acoustic data gathered by the UUV's sonar will then be converted into digital format and relayed to human operators on the mothership in real-time. Once the assessment is complete and the presence of mines is confirmed, the LCS will then deploy mine neutralisation equipment, as the UUV has no onboard equipment that would enable it to destroy the underwater explosives on its own.

The UUV was designed to operate as part of a complete mine countermeasures mission package (MCM MP) that is one of the standard mission packages available as installation options on the navy's Independence-class trimaran-hulled LCS. Each MCM MP will include two Knifefish UUVs along with support systems and equipment including low-frequency broadband sonar and automated target recognition software technology.

Alternatively, the Knifefish system can also be operated from other vessels of opportunity or even from shore control stations to detect and classify buried, bottom, and volume mines in high-clutter environments.

GDMS said the modularity of the mission package and rapid mission turnaround times will allow for platform flexibility and quick reconfiguration of the whole package in response to changing mission requirements that the UUV's operators are likely to encounter when deployed on combat operations. This means that a singular system consisting of two UUVs and support equipment will be adequate to enable an LCS to deal with the threat posed by mines to itself and other ships in the task force.

The navy plans to procure 30 Knifefish systems in all: 24 as part of LCS MCM MPs and an additional six systems for deployment from other vessels of opportunity.

The delivery of the first production Knifefish UUV comes after more than three years of testing, which also included trials against simulated mines placed at varying depths. A range of scenarios was implemented, including scenarios in high-clutter environments.

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