The U.S. military really wants a laser gun, and the Department of Defense is spending hand over fist to make that happen. Over the past 10 years, the Pentagon has funded an experimental flying laser cannon, built jointly by Boeing (NYSE:BA), Lockheed Martin (NYSE:LMT), Northrop Grumman (NYSE:NOC), and Raytheon (NYSE:RTN), to shoot down enemy ICBMs. It has funded solo projects as well, including:

Lockheed and Northrop's efforts to develop a laser gun capable of striking ground targets from the air

A "high energy laser" that Boeing plans to tote around on a Heavy Expanded Mobility Tactical Truck

A separate Boeing project to mount an advanced tactical laser aboard a warplane

A mirror-image Boeing project, dubbed "Laser Avenger," to shoot down unmanned aerial vehicles from the ground

Later this year, the U.S. Navy plans to conduct its most ambitious laser program project yet: test-firing a new naval Laser Weapon System, or LaWS, aboard a U.S. warship sailing off the coast of Iran. In the meantime, the Navy is working up a separate project, this time to benefit the U.S. Marine Corps. In an $11 million deal, part of the Navy's $58.7 million budgeted for directed energy weapons projects in fiscal 2015, the Navy just hired Raytheon to work on a separate laser weapon system. It will be "high power," "light-weight," and "rugged" enough to be fired from a small ground vehicle.

Carrying the exhaustingly long moniker "Ground Based Air Defense Directed Energy On-the-Move Future Naval Capabilities," the Navy's newest laser project aims to give Marines a mobile laser weapon capable of shooting down low-flying hostile aircraft and drones. The demonstration project will involve a 25-kilowatt laser gun mounted aboard a Humvee. Raytheon said it's confident that "in the very near future" it will equip the Navy and Marines with "increasingly higher power" laser guns capable of accomplishing a variety of missions.

What it means for investors

Why is the military all hot and bothered about laser guns? Aside from the "coolness" factor, lasers have two main attractions. First, they're cheap: Chief of Naval Research Rear Adm. Matthew Klunder said the very high-powered, deck-mounted LaWS will only cost "about one dollar to shoot." That makes it about 70,000 times cheaper than a single U.S. Army Excalibur artillery round (incidentally, also built by Raytheon).

Second, laser "shots" don't take up a lot of room in the munitions locker. Every bullet, artillery round, or bomb that the U.S. military wants to use in combat is a bullet, artillery round, or bomb that must be manufactured, transported to the front, and then somehow stuffed aboard a weapons platform for firing. All of this manufacturing, transportation, and storage costs money, and each round of ammunition takes up space as well. But a laser burst can be generated on site and is infinitely small.

So you can see how laser weapons might be much cheaper to produce and employ in combat than the traditional projectiles the U.S. military has been using since the War of Independence. Even after factoring in development costs, the savings from lasers could be significant.

A couple examples: During the 2011 Libyan conflict, the U.S. expended some $340 million worth of bombs, rockets, and missiles in supporting the battle to topple the Muammar Gaddafi regime. More recently, Israel went through some $225 million worth of Iron Dome interceptor missiles defending itself from rocket attacks in the ongoing conflict with Hamas. (And did we mention that Raytheon helped out with Iron Dome, too?)

If even only a fraction of such costs can be avoided by using nearly free laser beams, it will more than justify the millions of dollars the Pentagon is spending to fund laser gun research by Raytheon and its peers. This prospect will keep the research and development contracts -- and ultimately, the weapons production deals -- rolling in for Raytheon and the rest of the defense contractors.

And this is the big opportunity for defense investors.