VESSEL REVIEW | SXX3 – Fast, compact USV for littoral and coastal reconnaissance missions

UK-based maritime autonomy company JD Marine International (JDMI) recently unveiled a new type of unmanned surface vessel (USV) optimised for military and law enforcement applications, particularly intelligence, surveillance and reconnaissance (ISR) missions.

SXX3 boasts a compact size, measuring only three metres (10 feet) long, but nonetheless has self-righting ability and can operate over 50 nautical miles. The USV also features a modular design that allows it to accommodate various sensor payload combinations depending on operator requirements.

Despite its small size, the USV employs the same AI robotic control panel planned for use in larger USVs. This integrated approach ensures unified control over all onboard systems.

“It is a compact USV engineered for ISR operations in littoral zones and confined inland waterways,” Jonathan Reah, Design Director and Co-Founder of JDMI, told Baird Maritime. “Despite its modest overall length, the platform demonstrates exceptional seaworthiness, with operational capability in sea states up to level five.”

Durable construction for demanding operations and environments

The USV's hull is fabricated from high-density polyethylene (HDPE), providing superior impact resistance and durability. Reah said this makes the craft ideal for deployment in high-risk environments frequently encountered in military and security applications.

"Equipped with a level four autonomous control system, SXX3 enables pre-mission programming by a shoreside operator, allowing the vessel to execute missions independently with minimal human intervention. Real-time vessel tracking is maintained throughout the mission, with remote override capability if required.

"The onboard electro-optical surveillance suite – including situational awareness and dedicated ISR cameras – ensures continuous visual feedback to the operator, enhancing mission oversight and tactical responsiveness."

The USV was developed in response to user requirements for a lightweight, rapidly deployable vehicle that offers flexible transport options and operational readiness across multiple domains. The compact form factor enables expedited deployment and retrieval, supporting rapid-response scenarios.

"Engineered for durability, the HDPE hull structure ensures survivability in high-risk environments, while the high-speed propulsion system provides swift transit to mission areas," said Reah. "The integrated waterjet drive enables safe and efficient operation in shallow or confined waterways, enhancing the platform’s versatility in complex littoral environments."

The USV is powered by a Vetus VH 4.80 engine connected to an Alamarin AJ-160 waterjet. This configuration can deliver a top speed of 35 knots and a cruising speed of 25 knots, allowing the craft to conduct fast transits to adequately respond to developing situations.

All inputs from the radar, the compass, and other sensors run through an SM300 onboard computer supplied by Sea Machines Robotics. Output from the SM300 to the waterjet and engine is via Glendinning actuators while all signals are sent via a NMEA 2000 network.

All communications to and from the vessel is via a Silvus MIMO radio. Other key sensors include an Oculus 30X camera while space is also available for drone detection equipment.

The USV’s deck configuration and equipment can be tailored according to operator requirements.

Innovative design resulting in a lightweight but highly versatile platform

Integrating a full suite of autonomous control systems, navigation sensors, and a diesel propulsion unit into the compact three-metre hull presented JDMI with a number of engineering challenges.

"Given the spatial constraints, the design team eliminated the conventional gearbox and instead implemented a custom-engineered coupling to directly connect the diesel engine to the waterjet propulsion system—optimising both weight and space efficiency," Reah told Baird Maritime.

The initial configuration featured an HDPE deck and superstructure. However, combined with the mass of onboard autonomous systems, this configuration exceeded the vessel's weight targets.

"To resolve this, the superstructure was re-engineered using a custom carbon-fibre composite, achieving a weight reduction of approximately 150 kg. This modification delivered substantial gains in both top-end speed and overall manoeuvrability."

Extensive commissioning trials were undertaken to calibrate the vessel’s autonomous control system. This included iterative refinement of feedback control loops to ensure precise directional stability, responsive handling, and optimal seakeeping performance under dynamic marine conditions.

"Establishing robust partnerships with key suppliers—encompassing propulsion systems, electronic components, sensor packages, and autonomous systems—is critical to the successful integration and scalability of the platform," said Reah.

"Equally important is collaboration with experienced boatbuilders capable of delivering to precise specifications."

He added that supplier selection must prioritise proven reliability, adherence to delivery lead times, and the ability to support production scale-up in response to future high-volume procurement contracts. This ensures both continuity in the supply chain and readiness to meet the operational demands of clients in the defence and security sectors.

“Because they’re smaller and more efficient than traditional patrol boats, USVs use less fuel, require minimal maintenance, and don’t need life-support systems onboard,” Reah told Baird Maritime. “They also reduce the number of personnel needed to operate and support them.”

“Perhaps most impressively, USVs can stay on station far longer than crewed boats and can even be deployed in groups to cover larger areas or carry out coordinated missions like perimeter defence.”

Reah said that such craft can also operate in challenging or hostile environments and can take on high-risk tasks without putting human crews in harm’s way.