In the world of drones, airplanes get all the attention.

Run a Google search for "UAV" -- the popular acronym used to label flying drones that are designated "unmanned aerial vehicles" -- and the search engine will spit out 2.15 million results. But search for UAVs less popular cousin, the "unmanned underwater vehicle," or UUV, and Google can find fewer than 500,000 entries. 

In short, underwater drones aren't very popular yet ... but they're already "big in Japan."

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Japan isn't the only country looking to weigh anchor on underwater drones. Here's Boeing's experimental Echo Ranger, getting ready for sea. Photo: Boeing.

The Japanese and American navies -- together at last?
Last month, in a little noticed development, Japanese daily newspaper Yomiuri Shimbun reported that Japan will soon team up with the United States to develop a new class of unmanned underwater vehicle. (Japan's Defense Ministry denies the report, but the country recently gave its military expanded powers to cooperate with allied nations on defense matters -- and promised to spend nearly a quarter-trillion dollars on new equipment for its military -- so you have to wonder.)

While the actual participants in the new UUV might be uncertain, here's what we know about it:

  • It's small. Reportedly, the new submarine will be a mere 33 feet in length.
  • It's robotic. Yomiuri Shimbun reported that the vessel will be able to follow a "pre-programmed course."
  • It's "green." Powered by neither radioactive nuclear fuel nor dirty diesel, the robo-sub will operate on electricity generated by fuel cells.
  • It's independent. The sub will be able to travel away from a mother ship under its own power, swimming underwater for perhaps for as long as a month at a time before returning to base.
  • It's unarmed. Initial versions of the sub, at least, will be equipped with sonar that can help the boat identify threats while on patrol -- but no torpedoes to shoot.
  • It's cheap. Early stage development of the sub is supposed to cost Japan's Defense Ministry no more than $25 million over the next five years. The size of the U.S. contribution is not yet known.

What it means to U.S. companies
While not as high profile as their high-flying UAV cousins, UUVs are catching on in the United States as well, with several companies known to be involved in the development of "underwater drones" for the military. These companies could theoretically partner with Japan in development of its 33-foot robo-sub -- or compete with it. As such, for investors in these companies, Japan's project bears watching.

Who are we talking about, specifically? Glad you asked. The U.S. defense contractors working on robo-subs include:

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Scale model of General Dynamics' Knifefish. Photo: Wikimedia Commons.

  • General Dynamics (NYSE:GD)(NYSE:GD). Best known for building 60-ton main battle tanks for land warfare, General Dynamics is also a major player in blue water warfare through its marine systems division, which, according to S&P Capital IQ, did $6.7 billion in business last year. It's working on a 1,700-pound UUV for the U.S. Navy, which is called "Knifefish" and is designed for use in minesweeping operations off of Littoral Combat Ships (which General Dynamics also helps build).
  • iRobot (NASDAQ:IRBT). Better known for its robotic vacuums, iRobot moved into the underwater domain when it bought tiny Nekton Research for $10 million in 2008. Nekton makes Seaglider autonomous underwater vehicles (AUVs, an acronym still competing with UUV for primacy in military tech circles). At less than 6 feet in length, the Seaglider is just a fraction of the size of the 33-foot beast Japan is building.
  • Boeing (NYSE:BA). Better known -- much better known -- for building piloted commercial and military airplanes, Boeing gained a toehold in the UAV industry when it purchased ScanEagle drone-maker Insitu for $400 million (coincidentally, also in 2008). Since at least 2011, however, Boeing has been working on a new project: the Echo Ranger. At 18.5 feet in length and weighing five tons, Echo Ranger is just over half the size of the sub Japan is working on. But depending on the power source Boeing ultimately puts into it, the company says Echo Ranger could run twice as long before refueling -- up to 70 days.
  • Oceaneering International (NYSE:OII). The biggest name in underwater submarines today is Oceaneering International, which has been building submersible robots for years -- primarily for the offshore oil and gas industry. Oceaneering is also apparently helping Boeing to build Echo Ranger, in partnership with a third company, Netherlands-based Fugro.

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Echo Ranger takes a swim. Photo: Boeing.

The upshot for investors
Drones for the military are a billion-dollar industry -- dollars that to date, have been primarily tossed into the air to buy unmanned aerial vehicles. But as Japan's robo-sub project shows, and as the proliferation of unmanned underwater vehicle models among U.S. defense contractors further demonstrates, interest in underwater robots is increasing. Investors looking to get in on the ground floor of a new kind of military product -- one that counts 71% of the Earth's surface as its theater of operations -- would be wise to take notice.

Rich Smith has no position in any stocks mentioned. The Motley Fool recommends iRobot and Oceaneering International. The Motley Fool owns shares of General Dynamics. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.