A few years ago, Juliet Marine Systems (JMS) unveiled the Ghost, an angular boat that could actively reduce drag in the water by creating a bubble of gas around its two foils. Now the company has announced plans for the Guardian, a submersible version of the craft designed for both manned and unmanned military operations, on or below the surface.

Like its predecessor, the Guardian's active drag reduction system is based on the principle of supercavitation, where friction is lessened by the craft creating a bubble of air around itself. That in turn allows it a better top speed without using more fuel, and JMS says that at it's fastest – which is when it's traveling on the surface with four feet (1.2 m) between the waterline and the keel – the Guardian can hit 35 knots (65 km/h, 40 mph).

There's no word on its top speed when the craft is fully submerged, or how well the supercavitation works then, but JMS believes the option opens up more possibilities for the Guardian than the Ghost, aided by the fact that it can operate without the three-person crew of the previous model.

"We believe Guardian is the first surface vessel that is a fully submersible Unmanned Surface Vehicle (USV) and one that will meet or exceed the USV mission needs of navies around the world at relatively low cost," says Gregory Sancoff, President and CEO of JMS. "We expect it to transform the way navies fulfill their operational requirements in maritime technology and provide greater capacity in littoral operations, with a host of multi-mission capabilities encompassing intelligence, surveillance and reconnaissance (ISR); mine hunting; and anti-swarm, short-range firepower. There is no other platform like this in the world."

Measuring between 30 and 45 ft (9.1 and 13.7 m) long, the Guardian will run on a diesel powertrain with a hybrid electric drive. While none have been produced so far, JMS estimates construction would take between 18 and 24 months, and the craft will be standardized for easy maintenance and can be customized according to the needs of the customer.