The test boat was able to tail a target boat at 1 kilometer's distance, something military bosses say is a major step forward.

'Instead of chasing down these submarines and trying to keep track of them with expensive nuclear powered-submarines, which is the way we do it now, we want to try and build this at significantly reduced cost.

'It will be able to transit by itself across thousands of kilometers of ocean and it can deploy for months at a time.

'It can go out, find a diesel-electric submarine and just ping on it,' said Urban.

Diesel-electric submarines have nearly-noiseless engines, are incredibly difficult to track from afar.

The Anti-submarine Warfare Continuous Trail Unmanned Vessel, or ACTUV will be able to operate for several months at a time scouring the seas and coastal areas for silent, diesel powered enemy submarines.

Price tags ranging from $200-$300 million put diesel-electric subs within reach of smaller, volatile countries.

Russia has been selling diesel-electric subs to buoy its shipyards, triggering what some are calling an undersea arms race.

Reportedly, Algeria has ordered two, Venezuela is expecting five, and Indonesia will have six subs by 2020. Iran claims to have a fleet of 17 diesel-electric subs.

To spot the threat, Leidos developed an unarmed, unmanned vessel to shadow diesel-electric subs for months across thousands of miles of ocean and chase them out of strategic waters.

'Called the ACTUV, the unmanned boat can be deployed for months and track underwater threats for thousands of miles without human contact.

'It keeps our troops out of harm's way and also minimizes risks to the marine ecosystem by limiting the use of sonar,' the firm says.

It claims diesel-electric submarines are quickly becoming one of the biggest threats to naval operations and a $1.8 trillion commercial shipping industry.

'Detecting and tracking these stealthy subs presents a huge challenge even for the U.S. Navy, the world's most technologically advanced fleet.'